If a group allows Christians to join then I would never join it.
Do you really want to ban Christians?
No. I'm joking of course. I just don't like christianity and it's not because all these assholes in the past, took a few lines out of the bible 100 years ago, and then went about, killing religious people.
While I do understand your sentiment about Christianity and how the Church has acted in the past, it is unfair to exclude Christians. I do think that many Christians have something good in their hearts still, so what I suggest you do is to continue joining Christian groups and maybe you would find that it is not that bad actually.
I don't think Christians are good people. They have fucked over entirely too many people in the past.
You shouldn't just assume that every single Christian is bad because of things in the past. Pretty much every single religion or race has done terrible things in the past.