You're mixing issues here. As others here have pointed out, MLK chose a nonviolent path to fight a huge injustice. That was a very noble thing to do, and it turned out to be a great service to the country.
Now, does that warrant giving him his own day? It's not a slam-dunk for me. I would have been OK with it either way. But if I were forced to vote, I'd vote yes.
The second issue, the abolition of observance of Washington’s birthday and Lincoln’s birthday. Easy call there, for me anyway. That was wrong.
Is “social justice” non-violent? I think it indirect violence, treating people as a group rather than as an individual.
An issue with King is that a mythos has been erected which exceeds the man. He may have rallied people against racists - which is worthwhile - but that’s about it. For this we have parades, ceremonies, and push aside a Founder.