Well there are ways to rescue the more left-leaning non-libertarian positions without committing oneself to an absurd stance. For example, one could claim that we have a duty to help others and to promote the general good, and that using force against someone who violates this duty is permissible. That's not a position that is obviously unacceptable to some people (though admittedly, many would not be willing to accept many of the conclusions it leads to), and could be effectively defended by someone who had thought their position through well enough. Alternatively, one could accept the government's claim to ownership of its territory as legitimate, and argue that because we reside in that territory, we must abide by the contract (the constitution) that details the relationship between the government and its citizens. Again, I'm not advancing either of those positions, but taking either one would permit someone to be a liberal without committing to an absurdity.
http://libertarian-left.blogspot.com/