I've never seen a single Catholic on here complain that "Christians" are posting on Catholic threads. They might complain PROTESTANTS are posting on Catholic threads. Unfortunately for you, Protestants do not represent ALL of Christianity or even close to a majority of Christians worldwide (in fact, I believe there's about 25% of Christians overall.. roughly 400-500 million Christians are estimated to be protestant out of the 1.2 billion Christians estimated worldwide), no matter how much you want to pretend otherwise.
You can pretend otherwise all you want, like liberals pretending that conservatives oppose "reproductive rights" and deny "climate change" happens. No matter how loudly people make that claim, it doesn't mean there is a single conservative who says they against "reproductive rights", or any Republicans who "deny" that "climate change" exists, or any Catholics complaining that "Christians" post on Catholic threads. Your fictional talking points are not reality.
How would you recognize a Protestant and a Roman Catholic in a crowd? Perhaps you'd like it if non Catholics wore special clothing or an marker of some type?
I have no doubt y'all would love to have the Inquisition continue today.