What's with the denial?

In the After Abortion blog, there's a thread about the need to allow post-abortion women to move through their denial at their own rate.

My question is the denial that goes on in abortion advocacy. This is the example that springs to mind, and it's fairly typical.

One prochoice woman was insisting that abortion is only legal up to 12 weeks. I reached for the phone book, opened it up, and showed her the ads for the two abortion clinics in town. Both advertised elective abortions through 24 weeks. The woman just made a "hmph" sound and dropped the discussion. I later heard her discussing abortion with somebody else, and again she was insisting that abortion is only legal up to 12 weeks.

I can't quite fathom why she, and others like her, will pick a lie and cling to it with the tenacity of the damned. Why is it so important to so many people to believe with their whole beings that abortion is only legal up to 12 weeks? And how can they cling to that belief in the face of overwhelming proof that elective abortion is perfectly legal the whole way through the second trimester? I've had this very same thing happen online again and again. I'll be in a chat room or on a forum, and somebody will assert that abortion is only legal through 12 weeks. I'll post a link to prochoice sites that list dozens of facilities that do elective abortions to 22, 24, and 26 weeks. And these people will insist that the sites must be fake prolife sites!

What is with that?