One commenter, crowepps gave a good, illuminative comment on sexist assumptions about male and female sexual interest...
As I understand the psychology underlying this issue from other reading, and as evidenced by Paul's focus on the word 'intention', the problem is not so much the blastocysts, thousands of which are lost naturally all the time, but instead outrage at the idea that women seize the agency to assert that they have a right to INTEND to avoid pregnancy and still have sex.
As near as I can get into the mindset, it is that women should understand that FOR THEM sex is only a tolerable activity if pregnancy is possible because only the possibility of motherhood can sanctify a woman allowing her body to be polluted. In this worldview, there are only two possible reasons for a woman to have sex - because she wants to get pregnant or because she is depraved.
Men, of course, are recognized to have urges that impel them towards sex, sometimes disastrously, urges which create temptations impossible for them to resist. Women, however, are believed to be free physiologically of any such urges and able to easily and absolutely control themselves so that the default position of girls/women is to stay forever chaste.
On this biologically unlikely foundation is built the meme of the 13-year old girl's ability to rationally 'chose' whether or not she has sex, since she is assumed to have no interest in sex herself and no urges leading her forward but that instead all the impulse to go ahead comes from outside, from some male who is 'taking advantage of her' by using power, the lure of possessions or psychological judo to coerce her into a behavior in which she would otherwise have no interest. From here it's easier to understand those who insist that 'all sex is rape'.
-------End of Crowepps' words