To be fair...
King himself copyrighted a lot of his work, with the legitimate goal of using licensing to raise money for the civil rights movement. That worthy goal seems to have become twisted up over the years, though, by what looks like a combination of family rivalry and insecurity.
I'd be cool with the National Archives buying selected copyrights from the King family in order to liberate the works. What's a few $million amortized over all of humanity?