Rather to openly discuss religion or politics is simple. Are you open to a conversation, this doesn't have to be a drag out, pulling teeth out conversation.
It can be a simple way to break the ice when in countering someone new or your current conversation is at a stand still.
Usually there is always variables in ones tone that will let you know how far that part of a conversation is going to go. While both religion and politics can be cantankerous and volatile you never have to let it get that far.
Both topics can be a different animal. I myself fill very comfortable talking about my faith as a born again Christian. It's my responsibility to try and save as many lives as I'm able. Sometimes people wanna hear that calming word that holy spirit can give an open heart. When that topic gets to tight for an open ear it's time to move on, sports is always an easy out.
Now Politics these days is strictly black or white (no pun intended) and you chose your side. You must choose to agree or disagree then move on.