I understand that you think pro-choice speakers shouldn't be allowed on campuses of religious schools like Notre Dame because many Catholics are pro-life.
However, don't they have the right to free speech as much as you or I? No students would be required to go to such a speech on campus, so the speaker should be able to share their views on that campus, and students should have the choice whether or not they wish to go. If they do, they very well may learn something. Also, not all students who attend Catholic institutions necessarily are Catholic, and they do not have to be Catholic to go to a Catholic institution.
Furthermore, nowhere in the bible does it specifically say that abortion is a sin. Abortion has been around since biblical times - it is a very important issue, and a very personal issue. In fact, there are many Catholics who are pro-choice.
I went to a Catholic elementary school for 6 years, and many of my peers, over a decade later, including peers who remained in the Catholic school system through high school graduation and even into university (unlike myself to switched to public schools), are now pro-choice. In fact, I would say more of them are pro-choice than pro-life.
I think that a pro-choice politician shouldn't be stopped from speaking at Catholic institutions. Even if students don't agree, they may learn a lot about the candidate, the political process, and it may help them understand viewpoints other than their own. Whether they agree or not, they could gain a lot from the experience. It is completely reasonable for a pro-choice politician to speak at a Catholic institution, and I think that it shows that the politician understands their audience, and how diverse their audience is, by speaking at all.
Being pro-choice isn't just a religious issue. It is an issue of female bodily autonomy, an issue of individual liberty and choice, and choice that should be only for the woman considering abortion to make.