I can give one explanation.

Your organ example is one form of utilitarian paradox; we are indeed increasing the utilitarian good but at the same time do something that is intuitively wrong. One solution is grant basic human rights to everybody that are untouchable no matter what utilitarian good is achievable through sacrificing them. To me they could be right to basic physiological and mental principles. Utilitarianism is just one way to approach dilemmas which has its limits and nobody advocating anything of that sort will tell you to make it 'a golden rule'. Unfortunately your property is not entirely in the domain of basic rights from this approach.

One of the arguments that libertarians use is that one owns his or her body, thus one must own the fruits of his labor and by that line of thought pretty much everything one has acquired. I find this argument circular as you need to own the property you start with to truly claim the result as yours. Thus you have argument in which legitimacy of your property depends on legitimacy of your property... (Homesteading is of course one arbitrary way to explain this, but it is as absolute measure of property as to say: "you must not lie" is as a moral rule)

We have obviously a disagreement of values here. The stronger side (or the one with biggest guns in libertarian rhetoric) wins so I guess we won't see taxes going away for a while. Sad thing is that the result hardly matches anyones preferences.