It's easy not to have a problem with (c) when it doesn't harm you.
Item (c) is especially unfair as applied to single people: a single person earning certain levels of income pays significantly more tax than a person who is otherwise identical but who is married to a person who does not earn income. In effect, single people are paying higher taxes in order to subsidise married couples of equivalent income level. Under the current regime, this effect phases out at a certain threshold, but dragoncar's proposed changes would prevent it from phasing out and would be even more unfair to single people.
It's difficult to justify forcing single people to subsidise married people when you consider that being married already offers its own rewards: aside from having a constant friend and partner to share your life with, there are also numerous financial benefits (such as being able to earn twice the income without increasing expenses, thus dramatically reducing the length of the working career required to achieve financial independence). To be fair,
there are also certain risks, but most people appear to believe the rewards outweigh those risks. Anecdotally, most celebrated stories of people reaching financial independence early in life involve married couples.
In fairy tales, everybody falls in love and marries, but that's not how real life works. In real life, some people will never fall in love, will never have a romantic relationship, and will never marry. That is the cold hard truth of real life. Those people already have to work longer to reach financial freedom, and without the benefit of a lifelong friend, so why exacerbate the situation by also burdening them with higher taxes?
Under the Canadian tax system, individuals are taxed separately and married couples cannot combine their income for tax purposes, with certain exceptions that will not be discussed here. In
maizeman's other thread, he proposes bringing the same system to the United States. That is certainly an egalitarian idea. One problem with it, however, is that the US tax code does not contain a property law code. Instead,
property law is governed by state law. In certain states, including California (the most populous state), employment income earned by the members of a married couple is generally considered to have been equally earned by the two partners, regardless of the actual division of who did the work. See, e.g.,
Hunt v. Commissioner,
22 TC 228, 230 (1954) ("A husband's earnings from his personal efforts during the marriage are community property under the law of California. ... For purposes of Federal income taxation, each spouse is equally liable for payment of the tax on his or her respective
equal share of the community income.") (citation omitted and emphasis added). (Although the quoted language refers to a "husband", the gender of the spouse is not material to the proposition of law.) In other words, maizeman's changes would still mean that married couples would benefit from income splitting so long as they lived in certain states, including the most populous state.
In order to implement maizeman's proposed changes uniformly across the United States, one would first need to analyse the constitutional question of whether it is within the authority of Congress to override state property law for the purpose of the tax code and, in effect, "reallocate" income based on who actually earned it. That is fairly subtle question for a variety of reasons and I do not propose to analyse it in this post.