Money may be good when allocated fairly and productively, but "FU money" implies a sense of no obligation to society and in many respects is the motivating influence behind much of the ill greed rampant today. F FU money.
Because of that I don't share your interpretation that "FU money" is correlated at all with the sense of obligation. In my world view that obligation is intrinsic in the person and not affected by the source of income. When I see the good that the Bill and Melinda Gates foundation is doing, the Lucille Packard Children's hospital, and others, I think that is pretty cool.
[1] http://www.macfound.org/programs/fellows/
See: http://techrights.org/wiki/index.php/Gates_Foundation_Critiq...
So with his vast fortune Gates ensures that he pays the minimum required in taxes (which may support policies he disagrees with), and instead spends money on policies he supports.
That sounds perfectly rational.
If the perspective is that everything is disconnected and that you are more important than everyone else then yes, it does.
If one can see that all is connected and everything affects everything else then it makes very little sense. Those taxes pay for poor people's sustenance when they cannot work. They pay for people who can't afford private healthcare. It's rational to help them because more national unrest means more stress, less productivity and, in the end, less likelyhood of people buying your products.
The problem with being perfectly rational is that one may not consider the flaws in one's assumptions. Rationality is only as good as the information it's acting on and is not a silver bullet for making the right decisions. A blind man might conclude that while the sun may be hot at times, it's also extremely dark.
The point is that FU money is the point at which you have enough that you can walk away from situations that you don't agree with without that impacting the rest of your financial life in any manner.
In other words, it's retirement but at a younger age.
It's not to say you don't walk away from situations you don't agree with before you have FU money. It's just that you're at a point where it won't impact the rest of your financial life.
I don't really see why it has such a negative connotation.
/edit I should add this term is usually used in terms of someone who has spent 20+ years in a career (and typically the same company) and is at loggerheads with upper management in an unresolvable situation and is about to get forced out over the situation. i.e., upper mgmt is doing something that person believe is wrong, unethical, etc.