Give up money, give up fame, give up science, give the earth itself and all it contains, rather than do an immoral act. And never suppose, that in any possible situation, or under any circumstances, it is best for you to do a dishonorable thing, however slightly so it may appear to you. Whenever you are to do a thing, though it can never be known but to yourself, ask yourself how you would act were all the world look…
Slavery even exists in the USA - it's called the Internal Revenue Code; the only question is what percentage of the time while you are working, that you are a slave.
(Please note, I am not getting into what are usually called "tax protester" arguments.)