The axiom of finance is that having something now is better than having the same thing tomorrow. One who calculates by how much is said to discount. The same axiom holds elsewhere, but no one wants to do the math. The sacrifice that would be saintly if it were selfless is too often only thoughtless.
Take someone who refuses from a dish because of ethical objections about how it is now made. Someone who abstains from foie gras has made a permanent stand against an inherent evil, and means it. But someone whose argument begins “Do you know what kind of—” may not have weighed their position. You will not live forever. You are not guaranteed the ability to enjoy food even as long as you live. While you could still enjoy food, your health may forbid it. Whether or not you have bothered to count, at the end of your life there will have been only so many meals and far fewer good ones; are you certain you want to subtract this one?
Anyone who proposes to change the world needs to be asked: “If the world were as you want it to be, what would you do with yourself? Could you be doing it now? Why don’t you?” Perhaps the answer would deprive a worthy cause of a capable supporter; but if there is nothing good or worthwhile in the world except making what is worst in it less bad, then there is nothing good or worthwhile in the world at all.
(Besides, the most dangerous people in the world are the ones who try to change it without having learned how to live in it. Danton on Robespierre: Cet homme-la ne saurait pas cuire des oeufs dur: “That man couldn’t hard-boil an egg.” A man might become a monster only because he was good for nothing else.)
The taste for causes can be a jaded one. Helping people is one way of hiding from them. Trying to save the world is one way of giving up on it. Devoting your life is one way of throwing it away. You say the fruits justify the tree; but who would eat of it, if they knew how it grew?