It's not an unwarranted insult if it's true. That's a big "if". I disagree with much of what the Catholic church teaches and practices, as it is contrary to what the New Covenant is about. I won't go into the many ways that is the case, although I might at another time.
There were, of course, many churches other than those few mentioned in Revelation. John wrote to the seven churches that were in the province of Asia: Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia, and Laodicea. Of course, not mentioned are the churches in Jerusalem, Rome, Galatia, Philippi, Colossae, Thessalonica, and there were probably others. So when you say that they were the universal churches -- the catholic churches -- there is no Biblical basis for saying that. Nor is there any basis for saying that there was only ONE denomination, since Paul wrote over and over about the differences and errors made by the individual churches.
That sums up why I believe what the Bible clearly teaches, not what the Catholic church teaches. There are other reasons -- too many to list now -- but that's it "in a nutshell".
Sola scriptura!
