The Philosophy of Liberty is really the best, most concise, and most understandable explanation I have seen of how to determine what is right and wrong in the realm of politics. Any law that cannot be justified on the basis of these principles is unjust. Any time a freedom lover, anarchist, libertarian, or voluntaryist justifies force to violate these principles, he or she is making a terrible mistake.
I've seen people in these camps (or this camp) occasionally veer off of these principles for causes that might seem "left-wing" or "right-wing" or might not seem to fit into either category. At the same time, I've seen people who've never even seen this presentation follow these principles perfectly. This is what libertarianism is about (and all those other groups I listed above). This is what morality is about. Everything else involves initiating force against people who have done nothing wrong.