I sometimes think that the ability to share some uncomfortable topics is necessary for imtimacy.

But at the same time, such talking about uncomfortable ideas can also drive people away.

For me, the situation is always confusing. :-(

Maybe when I feel a genuine willingness to understand me without any judgement from that person. It's ralatively easy to find friends with similar interests, a good sense of humor, backgrounds etc., but great friends are there to help you even when you screw up. They are happy to share ups and downs of life with you. I think that's impossible without an open-heart and patience, which does not always mean to agree with you, but to support you howerver different you are. 

When we can talk about everything and nothing (is it right?) during hours.

Common topics and interests is necessary to have to become friends I think.