A person is not a Catholic because they attend a Catholic church (even if they do so regularly) or because they consider themselves a Catholic. They become a Catholic by being baptized into the Catholic faith. At that time (by proxy if they're baptized as an infant) they make a profession of faith. (And if they're baptized as an infant, they make that profession of faith later in life.)
That profession of faith has certain non-negotiable elements. One of those elements is that abortion -- the intentional killing of an unborn baby -- is never morally justifiable. Someone who rejects that is either rejecting the profession of faith they once made, or they simply never meant it in the first case.
In either case, they're Catholic only in the most superficial and legalistic of senses. They can repent and change that, but that's where they are for the time being.
So a person can't be a good Catholic and be pro-abortion. As Scripture says, "God is not mocked". They need to repent.
I should have written “can’t”.