I saw someone write this on a mailing list:
As a self-described left-libertarian (which means that I see human liberty and human cooperation as compatible, which the right-libertarians do not),"
There is no such thing as a left-libertarian OR a right-libertarian. Whoever wrote this is confused about libertarianism. Of course so-called right-libertarians believe that human liberty and voluntary human cooperation are compatible. If you believe in voluntary cooperation, then you are a libertarian, whether left, right, middle, top, or bottom. If you believe in any use of violence other than to prevent greater violence, then you aren't a libertarian. So-called left-libertarians believe in coercing desired behavior from peaceful people.
I think there's a larger issue here. "Liberal" used to mean the philosophy which is called in the US "libertarian", and which is still called "liberal" in some other countries. Since this philosophy generally promotes happiness and distributes power, people who seek power object to it. Since the philosophy is hard to understand and is counter-intuitive, it only takes a little bit of effort to undermine it. For example, you can introduce only beneficial coercion, bringing the philosophy leftwards. Thus, the "Liberal" is now applied in the US to the leftist trade-union high-taxes consumer-protection philosophy. By using the term left-libertarian, these people seek to convince people that libertarians believe in coercion. Left-libertarians are just ordinary leftists and socialists looking for cover. You can see this in the Wikipedia article on libertarian socialism. Fortunately, real libertarians are loudly objecting to their usurption of the term.