It is true that many cultures identify with a particular culture but religion itself is NOT culture. It's that simple.
I want to be really clear here. I'm not against religion. I am, myself, an atheist but if you want to believe in a higher being, feel free to do that. Just don't impose it's structure onto my daily calendar. If I want to celebrate Christmas, I can. That's a personal decision.
This is really about one of the principles the founding fathers (and mothers) set out for the USA and enshrined in the Constitution; the principle of the separation of church and state.
They don't go well together and result in prejudice, favouritism, stigmas and bias when that separation breaks down.
And that is something I will rant about from now until my time on this planet ends.