Sort of interesting you employ libertarian ethics for something like this. It's worth noting that most of the big names in intellectual libertarianism take precisely the opposite stance on abortion. Rothbard I know said that the fetus, even if we categorize it as a human, is a biological squatter on the woman and she has the right to expel it just as she has the right to expel a squatter from her land etc. You saying that sex constitutes consent isn't meaningful because (1) free consent can be withdrawn in libertarian ethics (i.e. if you let a person sleep in your house for a night, that does not mean you cannot tell him to leave the next night) and (2) even if that were true, sex acts that employ contraception by definition constitute means that specifically do not imply consent to child-bearing. I think if anything you're trying to take your already decided upon moral beliefs and trying to graft them upon an ethical system you pretend to accept axiomatically. You may think that abortion is morally bad, which I think is sensible, but because libertarian ethics, based on nearly nothing besides property rights and "natural law" etc. fail to make a coherent worldview anyway, you can't get anywhere. As I stated above, most hardcore libertarians are pro-choice in the most extreme way and it certainly makes a lot more sense with their ethics than anything else. The problem with those ethics is, as another poster noted, there is no sense of social obligation, not in some fuzzy social democratic or public welfare sense, but in the sense of the family and other traditional institutions. In private property rights and libertarian ethics, it is entirely permissible to not only abort fetuses, but to commit infanticide, neglect, or simply abandon children or members of their family. When your ethical system is based only on your infinite rights to production without any non-economic responsibility you don't really have a complete view of morality.