This argument is more a problem with society than anything else. They claim a faith because it's what their parents were and it's what they grew up with. They basically listen to it, but believe in whatever they want. Some of it matches, some of it doesn't. If every single person, at the age of 18, was to sit down and evaluate their belief system and compare it to every single religion, a ton of people would probably swap religions. But they don't, because they're comfortable enough with what they are and it's all they've ever known.
But back to what I said before, not every person fits 100% with any religion. You're basically saying that someone should change their religion because they're pro-choice. That's the most absurd thing I've ever heard of. That shouldn't have ANYTHING to do with religion! That was NOT a founding concept of Catholicism and didn't come about til the 1900's. If someone believes in every single little thing that the Catholic Church believes in, except pro-choice, you think they should find a new religion? What if Catholicism is still the one that works best for them? Stop being silly. Not everyone in your religion is going to believe in exactly what you do. Get over it and leave them be.
That life is sacred from conception til natural death is the doctrine of the CC. I can quote from the Catechism if you would like. For my part, I would like you to cite the document that says the Catholic Church was okay with abortion until "about the 1900's".
As for opinions on issues of concern to the church, there are some that are not opinions at all, and in fact are non-negotiable positions. Abortion is murder insofar as the Catholic Church is concerned, so if one claims Catholicism than they can no more support murder of an unborn as the murder of any other person. This is a defining doctrine of the Church, so someone should absolutely find somewhere else to worship if they cannot submit to the Church on the matter.
Abortion cannot be compared to opinions such as: head coverings at Mass or not, Latin vs. Novus Ordo, what to give up for Lent, Rosary vs. Scripture reading, etc. These latter examples are up to individuals to determine as to what works for their faith life.
Any opinion can go one way or the other and they can still fit the GENERAL idea of Catholicism. Who are you to decide what opinions can and can't differ?
