All churches I have attended use the flag as well. I'm just not convinced that it is appropriate (or inappropriate).It's not tied to that
It's not tied to that particular group. The flag is not owned, trademarked or copyrighted. That particular group only adopted it as their flag.
In the Churches I've been to it is used as a symbol of general Christianity and as a symbol that unites different denominations.
Some Churches even have a pledge that they use on it. I can't recall the exact words, I never learned it.
Us Southern Baptists had another flag....but we don't fly that one anymore.