Yeah, it’s a large part. Although, anecdotally most of the Catholics I know tend to be pro-choice (this is probably just selection bias, though).

Interestingly, the Church’s anti-abortion stance is doctrinal, but has not been proclaimed by the papacy in an ex cathedra statement or as an essential matter of the faith. A lot of Catholics treat it as one of their faith’s “matters of conscience” and form their own personal opinions on the matter.

Roman Catholicism finds itself in a very awkward place with regard to abortion. The Church itself was the creator of the concept of Social Justice and many of its faithful (rightfully, imo) seek to apply a similar philosophy to the topic of abortion.