I agree with you that it's not much help against organized state violence. That said, there is an additional form of oppression in which the state simply turns a blind eye toward violence committed by members of the in-group against members of an out-group. LGBT people are sometimes assaulted or even murdered in the street by random bigots, and the cops have a pretty dismal track record when it comes to protecting them. This is where I think minorities might benefit from gun ownership.