Liberals/leftists/progressives often get accused of 'moral relativism' by the knuckle-dragging set. For the most part, this charge is baseless (no surprise there); however, I think some on the left too often unwittingly reinforce this perception.
For example, Kos has written a couple of posts comparing the Religious Right to the Islamic fundamentalists that right-wingers profess to hate so much. He concludes by saying:
The reasons we hate the American Taliban are the same reasons we hate fundamentalists of all stripes -- they seek to impose their own moral code on the rest of society, and do so with the zeal and moral absolutism possible only from those who believe they are doing "God's work".
I, too, am disdainful of both Christian and Islamic fundamentalists. But there is nothing inherently wrong with trying to impose one's moral code on others; nor is there anything wrong with doing so zealously or with absolute conviction; nor does such zealousness and conviction require a theological foundation. Indeed, imposing our moral code on others is precisely what progressives want to do. It is the motivation behind things like the Universal Declaration of Human Rights. Universality has been a fundamental feature of moral reasoning for centuries, and was codified perhaps most convincingly by Kant, who correctly argued that any moral imperative necessarily commands universally (categorically). Non-universal norms are not moral norms.
Of course, it is not always okay to impose one's moral code on others. For instance: I might believe that everyone has a moral duty to take care of their health, but that doesn't mean I should try to pass a law against smoking or eating Twinkies. But there are other areas where the presence and nature of a moral principle clearly dictates that one be willing to 'impose' upon others by codifying the principle into law - for instance, Jim Crow laws were morally abominable, and decent people did not hesitate to enforce their moral code upon segregated communities.
The reason that fundamentalism is reprehensible is not that it tries to impose its moral code on the rest of the society; it is reprehensible because the moral code itself is reprehensible. The 'moral' principles of Osama bin Laden - and of James Dobson - are irrational, misogynistic, backwards, and cruel, and so we rightfully resist their attempts to impose them on the rest of us - not because of the fact that they are trying to impose them, but because the principles themselves are evil and idiotic.