Maybe because it's a sweeping generalisation that doesn't actually apply to many people.
I know that the right wing press love to generate antipathy to anyone who receives state benefits but people don't generally wish others to be deprived, nor do they create elaborate fantasies about their past. A few do, maybe, but most people don't.
It's how people actually vote and lobby. It goes far beyond state benefits. I call it the "I got mine, so forget you" mentality, and it is common to both the left and the right. No gender, generation, ethnicity, creed, or political perspective is exempt.
I'll illustrate, using examples that don't involve money.
Millions of people spent the 1960s and 1970s getting drunk or high and having fun. Some of them were in college. Others just saw a need to behave as though the word "party" was a verb. They had the benefit of whatever alcohol and drug experimentation was necessary to their personal development, and the vast majority eventually outgrew the "party" mentality and got on with their lives *without* any lifelong legal consequences. Once they reached that stage, they used their demographic majority to elect and support legislators who cracked down on the same behaviors they themselves had engaged in: underage alcohol experimentation, recreational drug use, and such. This did not really affect the next generation's experimentation, except that now that those activities were criminalized a college-aged young adult who did exactly what his parents and grandparents did would be hit with a felony conviction and possible prison time. The children of wealthy families mostly avoided that penalty, so it fell disproportionately on young people from poorer families, and families of color in particular: a felony conviction makes a person ineligible for all kinds of jobs and other opportunities. Meanwhile, having large numbers of potential competitors locked up or legally ineligible for certain kinds of work makes the job applicant pool smaller. This creates far more plentiful opportunities for the people who do *not* have convictions (either because they were raised in a way that allowed them to avoid exposure to the illegal thing, or because they were able to avoid getting caught, or because they were able to avoid punishment after being caught). But you will almost never see a person who gets a job that requires a clean criminal record, a clean drug test, or any kind of background check acknowledge that their opportunity came as a result of any factors other than their own hard work, sacrifice, and moral rectitude. Once they are in an environment where their hard work *can* produce rewards, and once their hard work starts to pay off, people get used to it. In fact, they assume that the reward-for-work relationship is universal (even though it isn't). The notion that there are destructive behaviors that ought to be punished starts to seem reasonable, and the fact that they, individually, have Straightened Up and Flown Right makes it easy to justify withholding opportunity from people who, by virtue of their felony convictions and lifestyle choices, have failed to do so.
Today's biggest young liberals, the modern equivalents of the hippies from the 1960's and 1970's, seem to believe that they will not succumb to the exact same change of perspective. Maybe it's because they have not yet gotten theirs that they regard the "forget you" part as bad or inappropriate. Or perhaps it's because they haven't been seriously tested yet. I think that, in time, large numbers of them will succumb in turn to human nature. There will be outliers who don't, of course, however recent history suggests that most of them will kick the ladder away sooner or later.
Many people benefit from safe and legal abortion, and it goes far beyond the very extreme cases of a baby with medical problems who is doomed anyway or a pregnant woman in medical distress whose life cannot otherwise be saved. We all know examples of female people who benefit from avoiding the pain and responsibility of a pregnancy at a critical time of her life, and from avoiding the medical expenses and debt that go along with pregnancy and delivery. I won't repeat these cases here because we've all heard it. But there are male people who benefit too. Consider the college student or trades apprentice who is allowed to complete his education without having to drop out and work to pay child support. Consider one of the recent candidates for a major party's 2016 Presidential nomination: a medical doctor whose educational credentials were based in part on research using fetal cell tissue, who made the *banning* of such research a part of his platform. Consider the people whose lives have been saved and improved by fetal cell tissue research, some of whom are male. Consider the hardworking father who is already working as hard as he can to provide for his wife and children, some of whom may have special needs, who simply cannot afford to feed even one more mouth. Consider also the children from such a family who continue to receive a share of their parents' time and resources. Some of those indirect beneficiaries are male too. Yet doesn't seem to stop them (or female people who have benefited from an abortion either directly or indirectly) from aggressively voting and lobbying to prevent other people from benefiting in a similar way. They've already got theirs, so forget everyone else... and pretend that their own hands are somehow clean when they aren't.
People who vote in favor of laws that criminalize behaviors they themselves have engaged in or benefited from, and who do not immediately turn themselves in for the appropriate punishment, are pretending that their own behavior or shortcomings didn't exist (false personal narrative) or that it was somehow more justified or less serious than someone else's similar behavior (rationalization). That's hypocrisy no matter how we slice it. But the urge to throw that first stone is part of human nature. So is the urge to rewrite history a bit so that the person who wants to crack down on others while simultaneously avoiding punishment. The proof? Witness the absence of an avalanche of Baby Boomers thundering into the local police station to turn themselves in or even pay the fines related to their own drunk driving or drug experimentation back in the day. They didn't do it in the "Just Say No" era, and they aren't doing it now even when the punishments for drug possession and use are much lighter.
Now let's consider civil rights. Anti-discrimination, which includes the anti-segregation initiative, enjoyed broad support from people from every ethnicity and sexual orientation. People of all sorts gathered under Reverend King's banner, and his message-- religious though it was-- was so full of common sense and objectivity that it eventually prevailed... partially. The right to non-discrimination based on race made it into the Constitution, but not non-discrimination based on sexual orientation. Why? Well... after Reverend King's death, it turned out to be a case of "support me getting my rights, because Religion" turning into "Thanks for the help getting me my rights, but I can't support you getting yours, because Religion." In other words, "I got mine, so forget you." The struggle for LGBTQ equality has been mostly without support from churches of any sort, and coincidentally without much support from most mainstream Black communities. This has made life even more difficult for LGBTQ people *from* religious and/or mainstream Black communities, because they get "forget you" from even more angles, including their own parents and family who can and do wish for them to be deprived of the benefits of things like legal marriage. In fact, in some circles it's still fashionable to expel a gay son or daughter from the family or at least make sure that they never get to bring somebody special to Christmas dinner.
It might have seemed intuitively obvious that non-straight people, having so recently been on the receiving end of I-got-mine-so-forget-you, might be more sensitive to it. But they're not. First, gay men and women immediately turned against bisexual people and made them into second-class citizens within the gay community. It's because people who experience attraction to individuals of more than one gender are a threat. If equality is being fought for, and won, based on the argument that sexual orientation is innate and not a choice (which is true for many people), then the presence of even one person who even *appears* to have the option of a choice is dangerous. For this reason, bisexual and pansexual people are relegated to second-class citizenship within most gay communities. They not welcome in most gay clubs or social circles, although straight people are. Most gay people, and most straight people, refuse to date or marry a bisexual person because there's an unfounded stereotype about bi people being incapable of emotional attachment or commitment. It's still OK to stigmatize bisexuality as being synonymous with immaturity, disloyalty, adulterousness, promiscuity, and psychopathy. For details, see every Hollywood movie featuring a bisexual person, ever. Furthermore, there are gay people who, after benefiting financially from the last four years or economic boom in the stock market, voted in favor of their pockets even though the administration that helped create and perpetuate that boom was aggressively targeting people of the same sexual orientation as themselves. They were well enough educated, wealthy enough (balance sheet AND income), and well enough connected to not be in danger of significant personal harm even if all the non-discrimination law was magically erased. In short, they got theirs, so forget you.
If you add up all the people who seek to criminalize what they themselves have directly or indirectly benefited from, or who have benefited from a lift up the corporate or social ladder only to intentionally exclude some of the people who helped to boost them, unfortunately what you have is the majority of human adults. That's how it's been in the past, including the recent past: "I've got mine, so forget you" is an immutable part of human nature. For that reason, I believe that the future will continue to be *exactly* like the past.
Unless. (I can do this because the Lorax is manifest in my living room.)
Every individual person who rejects the "I got mine, so forget you" mentality has the power to turn around and empower others. If every one of these raises up two (or preferably three) more people who would otherwise not get an opportunity-- and understand that our own kids don't count because they already *will* get that opportunity-- it's a start. If everyone who is so lifted and raised turns around understands that they have the duty to do the same for two to three others, and passes along both the opportunity and the obligation in three ways, what we will have is an exponential chain reaction that could, if left unchecked, encompass the entire globe.