If "libertarian" means it's a-okay to tear babies limb from limb by abortion, and that man marrying man equals many marrying woman, please count me out!
Most libertarians use natural law as the basis for their political philosophy. Many would oppose abortion for the same reason they oppose the death penalty. They do not believe that the state should ever have the power to take human life. And most libertarians would say that marriage is not a matter for the government to "license" one way or the other. So libertarians are not so different from many religious fundamentalists on these two issues.
Of course all libertarians aren't united in their views, but going with the basic philosophy, abortion is wrong because it is violence against another human being. Gay marriage is solved because the government shouldn't be in the marriage business anyway. Sure, let people do civil unions for tax (although that mostly goes away with a Fair Tax) and other legal purposes, but true marriages (heart and soul under the deity of your choice) are up to the churches, mosques, covens, etc.
It doesn't mean that.