Are the more non-religious people those who most recently quit religion?
If so, it's reasonable to conclude that the most vigorous disputes are those between:
1) those who changed a belief yesterday, and
2) those who will change the same belief tomorrow.
It all depends on what you mean by closed minded. I for one am closed minded about unreason and illogical ideas
I was a very closed-minded atheist for a few years until I learned the last person I ever thought could believe in god noted he was a believer. That threw me in for a loop.