[PhasmaFelis]

Because I would like to live in a functional society. Because "my right to a third yacht trumps your right to feed your children and get treatment for preventable illnesses" is a shitty thing to believe. Because I think the members of a society have a positive responsibility to each other and to the society. Because, basically, I don't like selfish assholes, not matter how much they try to convince me that selfishness is a virtue.

It's not a popular opinion, I realize.

And before you start talking about "other people's money," I'm comfortably middle-class, and I would be delighted to pay an extra, say, 20% of my income in taxes if it meant that the sick or homeless or mentally ill people I see every day could get the care that they need.

[grinnbearit]

Popular opinion or not, selfishness and generosity are calibrated by your moral values.

You're proposing an economic transaction where X pays, Y benefits and your moral desires are fulfilled. I doubt X would have a problem with you donating 20% of your income to a charity of your choice, why do you have a problem with their yacht?