Some people think you have to be evil to work in PR, but it was as a teacher that I faced my first and so far last serious work-related ethical quandary. The three semesters I taught composition, I regularly had to choose between (a) teaching each student equally and according to hir needs and (b) not helping anyone be more persuasive in arguing for blatantly bigoted things.
I always tried to do (a). I taught more than one student to avoid the opposition's buzzwords when they advocated for "separate but equal" unions for same-sex couples. I was shocked the first time to discover that someone could know that phrase and not know it was code for institutionalized racism, and therefore not likely to win any sympathy to the cause (I hope).
Those students who used my suggestions crafted subtler arguments, the sort that might actually persuade you that separate but equal really is equal without your being aware--if you weren't already firmly committed to equal marriage for couples regardless of sex. I don't think there should be any legal institution of marriage, but instead an adult domestic contract that carries no obligation of romance or sex. Who wants the government involved in that? But I digress.
I don't know if I felt worse about the successes or the failures. The students who tried to write and argue better, but something got in the way. The students who didn't try--I suspect most believed my feedback was based on divergent beliefs, which happened with papers I on the whole agreed with, as well. However I glad was a student was advocating equal rights for queers, I just had to take points off for arguing that the bible is invalid because it's old. And in case anyone's wondering, however despicable I found the content of a student's argument, I had to give points for being argued well.
Though that conflict was only one of the reasons I stopped teaching, it's a little amusing that an ethical quandary in teaching led me to be in the right place and time to get a job that led to my present one in PR, where, at least with my employer and position, my principles haven't been called in any notable way into conflict.