Depends on the person.
It can be very difficult to have a conversation with religious people.
But I'm sure they feel the same way about non-religious people.
I have some "friends" that are religious, but it is difficult to really talk to them about anything. We tend to stick to neutral topics such as Cars, Computers, Sports, etc.
But I can't really talk about anything meaningful with them because our views are so fundamentally different.
Try convincing a law student that the legal system is wrong.
Or try convincing a conventinal doctor that he shouldn't practice medicine, but should just sprinkle herbs on his patient.
etc etc etc.
Everyone has their own beliefs and any time you meet someone who's beliefs are fundamentally different it's going to be hard to talk to that person.
I personally enjoy the debates when I can find a reasonable person to discuss with. But it's certainly difficult to have friends among the opposing groups.
As for extremists...well you get extremists in everything...and by and large they aren't really good for much.