The problem is, we already have this situation where some irresponsible parents squander their welfare benefits now, under the current system. The real question here isn't whether some people will "waste" their UBI benefits at the expense of their dependents; there is no doubt that some will, unfortunately. And the reason why we know for a fact that some people no doubt will waste the money is because some people currently receiving money already do waste it. So the real questions to my mind are the following: 1) would the squandering problem under the current system be better or worse than the squandering under a UBI system, and 2) even if the squandering would be worse under UBI, do we morally have the right to restrict everyone's spending by force, even the spending of the vast majority of people who would use the money in accordance with what we consider to be "proper" values, just because of the fact that an unknown but significant minority is going to choose to fuck up their own lives and the lives of their dependents?
I don't particularly want to live in a society where the lowest common denominator among us gets to dictate what you or I get to do....not to mention the concern that power corrupts, and the more power we give to government (which is, we must remember, a monopoly on force), the more it will continue to appropriate for itself. Not saying there's an easy answer to this issue....but more government "programs" has yet to be a successful solution. After decades of our war on poverty, war on drugs, war on (fill in various other social ills here), we still have just as much poverty and drug use in our society as ever. And ultimately, it comes down to what we believe about basic human nature. I honestly do believe that most people WOULD make better decisions for their lives than nameless, faceless, unaccountable government bureaucrats would make for their lives. No government bureaucrat cares more about a person's life than that person does. And that person's right to self-determination should not be subject to bureaucratic whims just because a few other people will make bad decisions. That is ultimately the root of my support for UBI.