He was a great man, and a pig. Many great men are pigs.
Oskar Schindler, by all accounts a pretty base character, still was a great man in one matter—a very important matter. God doesn’t always pick saints to do His work. For all of his faults, MLK did do great work in deinstitutionalizing racial segregation in this country. That said some are doing their best to bring segregation back—see safe places, special graduations, etc. etc.