I think perhaps you should read more of what Dr. King actually advocated for and said. He didn’t endorse violence, but he didn’t condemn it either. He typically didn’t come from it from this moralizing angle either, most of his emphasis was his belief that violence was first and foremost a poor tactic, but at the same time he understood why violence happens. You’ve probably heard his 1967 statement “a riot is the language of the unheard.”
I know this is just a forum and the libs are always confused by nuance, but exploitation does occur in socialist countries, just in a vastly different character and at a much smaller scale. Cuba for instance does have private land owners who employee workers, and China of course has various large corporations.
However these are symptoms of the positions the nations find themselves within. Socialist nations tend to find themselves in the middle of capitalist encirclement. Until the last capitalist is extinguished, class based exploitation will continue to exist.