They start fights among friends. Have you noticed that? When I grew up there was a saying. It was "Don't discuss religion or politics." Why? Because, like I said, it started good friends hating each other.
When I moved to California I was registered Democrat. After Jerry Brown's first term, I became an independent as a protest gesture. Then I realized I couldn't vote in a primary (this was true in California in the 1970s). So I registered Republican so I could vote in a primary and I could vote for any parties or independents.
Why do people fight about these things? I've seen great friendships ruined with arguments and fights about politics, religion, and sports. All I've got to say about that is what Bob Newhart said in his famous psychiatrist bit: "STOP IT!!"
Oh and, no, I have not had any fights about politics, denominations, or sports teams in years! I just keep my mouth shut and say, "That's interesting."