This is one of the most idiotic, deranged arguments I've ever heard. Let me help you out:
1) the KKK was not Christian.
2) Conquistadors? If they raped/killed/enslaved people, then it's completely irrelevant to this conversation because those aren't Christian activities.
3) The Atlantic slave trade was not by any means a "Christian cause".
4) The Salem witch trials, ok, I see. You're an idiot. Just because there were some paranoid Christians a long time ago who killed some old ladies does not mean Christianity is bad, in any way. It's an illogical assumption.
5) ah, the Holocaust. I bet you'd be surprised to find out that Hitler's anti-semitic ideology did NOT originate from Christianity, but rather Darwin's Origin of Species. He believed non-white races were evolutionarily inferior, and so did Darwin. If I remember correctly, Darwin called for the extinguishing of all non-whites.
6) my point is, just because you're stupid doesn't mean you have to stay that way.
You can realize, like the average human being would, that just because something was done in "the name of Christianity", doesn't mean Christianity was actually even involved.
Like I said before, you literally don't know what Christianity even is, so you shouldn't be talking about it.