My personal belief is that these sort of threads are spammed by a handful of rabid pro-aborts trying to make their presence felt. It's generally the same aethiests, libertarians and leftists who make the most noise. I don't take them as any sort of serious representation of FReepers in general. Just activists, toting the same Planned Parenthood party-line you hear from the feminists on the radical left.
I'm not sure what is the bigger obstacle, sentiment or the institutional power of the proponents of infanticide. Given modern polling, I'd venture the latter.
Change the sentiment and you take away their power. And don't be so sure what the polling data will show. The last few polls, including a recent CNN poll, show a 50/50 split on the issue. And if you break down the "Pro Choice" camp, you'll find that half of them are morally conflicted on the issue and believe in certain state-regulations (hence, 75% of Americans supported the PBA ban).
Notice how infrequently polling data on abortion is released these days in the media? There's a good reason for that.
Take heart. The tide is turning.