Why are you (still) a Christian?

[Mister Agenda]

I thought anti-theists were just against theists.

Technically, anti-theists are against theism, not theists. They think no one should believe in any gods, but it doesn't imply they would do anything 'about the theists' in additon to just being disapproving of their theistic belief.

Even more technically (and definitely more pedantically), you wouldn't actually have to be an atheist to be an anti-theist; you could believe a god or God exists and also think no one should believe it. I'm not sure there actually is such a person in real life, though.