One principle that libertarians can adhere to is that there is a relationship between action and consequence, that is, responsibility. One of our fundamental ideas is that the bulk of our problems are caused by governmental actions that tend to separate action and consequence. This principle underlies our opposition to welfare, unemployment benefits, single-payer healthcare and a long list of other things. Yet, we are reluctant to hold women responsible for their conception choices. To me this is an inconsistency.
All actions carry risk.
This is why we oppose the IMF as a mechanism to unilaterally impose the risk of unsound investments by banks on US taxpayers. The pursuit of happiness coupled with taking the liberty to not use conception control bears the risk of generating a new life. Destroying that life is a unilateral transfer of risk from the woman to the fetus. In a political system, risk always devolves to the weak. Libertarians should be championing a moral system that protects life unambiguously.