Intersting views here. I have met Catholics that consider themselves Christians. I guess some Catholics don't. But for the same reasons given that swiitching from Catholic to insert denomination would be considered switching religions any denominational switch could be considered switching religions. If you go from denominational to undenominational is that changing religions? The basic beliefs of God the Father, Jesus, and the Holy Spirit have not been rejected. The belief that Christ died for our sins has not been rejected. The belief in heaven and an afterlife have not been rejected. What has been rejected, to me, is the process of how to worship and achieve eternal life. The basic belief system still stands.
To the first bolded, it's cultural/historical because after the protestant reformation, some people were no longer "catholic," right? Surely, catholics are christians. They receive the body and blood of Jesus...the actual...yes. But they are not protestants who are of a different religion. Religion is belief and practice. Of course, catholics and protestants worship Jesus but protestants do not have the full faith (please do not take offense...it's an explanation) as handed down from the apostles. They have Jesus, surely. But they are not under the fullness of the catholic/orthodoxy. It includes the eucharist...that is central. This is not a value judgment at all...just explaining and very briefly so. It's way more complicate than just that.
To the second bolded, yes, it is changing religions. Non-catholics may not take the eucharist. Catholics may not take communion in protestant churches. Catholics may not marry non-catholics without a proper church-issued dispensation. Etc. It's about accepting the entire Church, it's traditions, it's doctrine, its bible, everything. Incidentally, if I entered St. Mark's Church which is the Coptic faith, I'd have to convert. They would not consider me, a catholic, as a "true" follower of the one true Church. BTW, their church is so old in tradition...they have not changed Roman Catholics have changed up the service a bit...but the eucharist...NEVER EVER changed. NOt from Chaldea, Orthodox, Aramaic, Ethiopian, Byzantine....in other words...the first church and the eucharist, never changed. Protestants are not a part of this. Their communion is not transubstantiated (I'm tired this evening..please google for full explanation). It's about taking up the entire Church and not cafeteria style. It would definitely be changing religions. They are not the exact same...between protestants and catholics, orthodox etc. Of course, there is a little historical problem and in-fighting that maintains East and West...and a little prejudice as well.
between us catholics and orthodox.
Basically, we are all G-d's children. One day, we will join with the synagogue...there will be one worship of all mankind of the One True G-d. We should all respect each other's freedoms to follow G-d as they are chosen, acculturated and so see individually fit. I'm about to keel over from fatigue. Until tomorrow, by G-d's will.