Well, I'm okay with imposing cost-sharing between both biological parents...AS LONG AS both biological parents have the legal option to sign away their parental rights/responsibilities prior to the birth.

Of course, if the pregnant woman doesn't know for sure who the biological father is -- should multiple male sexual partners be forced to submit to (and finance) DNA testing against their will?

The ethics that you mention are a matter of personal conscience, not legal mandate. I personally have no ethical objections to a woman's decision to terminate the pregnancy.