Proposing violence to fix an issue with which appears your friend is not well versed on seems just like the mass mob lynching of a “suspected” person doing X. The mob feels righteous at the time, only to learn the person killed didn’t do anything at all.
Stating that as the basis for a debate is not the same as endorsing violence as the fix. It seems to be a tragic fact that different societies have not found a political way of solving this issue and that alone is worth discussing.
I think that's wrong, though. Poor people do not have the resources to wage war. Wars are led by people with resources against other people with resources, with poor people only serving as cannon fodder. That also holds for revolutionary wars, e.g. pretty much any Communist revolution was led by middle-class intellectuals. So I think that inequality might increase criminality and strengthen violent gangs, but it's unlikely to lead to actual war.