But is a said before the christian mentality that they are better than everyone else.
I never came accross that one, and it sounds like you're straying into the territory of "the white mans burden" and all that kind of rubbish. That is to say, you're confusing christianity with imperialism, because most of the imperial oppressor type of nations were european "christian" powers. However, nobody ever enslaved whole nations for anything other than money and power, whatever might have been claimed with regard to spreading christianity while they were slaughtering the locals.
Anyhow, I never felt superior to anybody until I read your original post and..(JOKE!)
Actually, I'd love to say you're wrong about Christianity and Aikido clashing, but what do I know about aikido? (answer- very little.) I'll just say I've never spotted it, and I think maybe your interest in aikido is really unrelated to your dislike for christianity. Maybe.