You may be overestimating how familiar they are with the specifics of IVF. It could be perceived as simply as “IVF means more babies, which is good, because I want babies. But abortion means less babies, which is bad.”
If those people like that perception, they will resist or deny any further detail that would jeopardize those perceptions to remain willfully ignorant, especially if they have utilized IVF themselves. The cognitive dissonance would be too strong otherwise.