I don't think Brits feel uncomfortable talking about god for fearing of having a debate. I think it's more that we don't really consider religion a suitable topic of conversation in most circles. It's a private matter and should be treated as such.

To employ a cliche, it's probably part of our British reserve...

I don't really know why I say 'we' there - I'm not even a proper Brit, and I don't find talking about god uncomfortable! In fact, I take great interest in it!

(I'm an atheist.)