To the title question: is abortion a mortal sin? A solid “maybe.”
Paragraph 1735 of the Catechism gives a sample of reasons why a grave action may NOT be a mortal sin or even a venial sin.
If a woman is forced against her will to have an abortion, then she did not have free will to decide, for example. If she didn’t know it was “wrong” then ignorance is a factor against this being a mortal sin.
The Catechism is the “deposit of faith” so Catholics must believe this and accept it. I ha ve read the entire catechism a couple years ago and I don’t remember if anything was automatically called out as a mortal sin. Instead, the CCC does call things a grave action, which is only one of the conditions for a sin to be mortal.
One of the things in 1735 is “inadvertence” — so follow me on this – the other things on the list may include things that we knowingly and deliberately do, yet they may not be a mortal sin.
So, there’s a problem here. Who decides if it is a mortal sin, in the end? Fr. Riccardo of the Detroit area on EWTN radio sais that he cannot judge whether a sin is mortal, because of the complexity of para 1735. In the confessional, he is not qualified to look into anybody’s soul or even into the circumstances of a sin to tell if it is a mortal sin. The same would apply to a bishop or the pope, would it not. I conclude that it is up to a person examining their conscience to decide whether something is a mortal sin. If you “punt” and say just confess everything, well, OK, if you want to. But I think those words are in the CCC to help you decide, even though there’s not much guidance on how to make that decision.
There’s a TV priest that has given very narrow guidance on this para 1735, but I think it was misleading. I have written a letter to the US Conf of Cathoilic Bishops on how to understand 1735 and they did not reply. THAT’S why I say it’s up to you to seriously examine your conscience to decide for yourself – lacking further guidance from the clergy.
Hope this helps.