If a "pro-choice" essay had been under discussion, then "LessWrong is already pro-choice, of course it's not going to be a mindkilling discussion" would have been my conclusion as well. But the thesis of the essay was strongly "pro-life", and it still got a good reception, with rebuttals mostly of the form "here's what's wrong with your assumptions and numbers" rather than "go away you woman-enslaving theocrat".

It could just be that the survey questions don't distinguish between different reasons for various stances? There may be a big practical difference between "I'm strongly pro-choice because analysis of this complicated moral question heavily tips that way, so I'm open to reconsidering if my reasoning is weaker than I thought" and "I'm strongly pro-choice because there's no good more-moderate Schelling point, so any attempt to undermine my position must be fought like a camel's nose in the tent."