In before the haters...the Founders weren't spotless but we (rightly) revere them for what they did. We often speak first of their writings, the Declaration, the Constitution, how they put it all on the line so that WE could have a better life. We then acknowledge that they were not perfect, often owning slaves and other conduct that was unbecoming, but we ultimately agree that they were a net positive element in the universe.
( HT leaning right). MLK is in a similar camp. Yes, he didn't help found America and I'm not equating his work with drafting the Constitution. But the man took a bullet for basically saying we should judge our fellow man by the content of his character, not the color of his skin. But wait, some say...King evidently had serious issues with prostitutes. Well, George Washington owned slaves. And Andrew Jackson mistreated Indians. And Ulysses Grant was a drunk. Etc.
Trotting out out MLK's deficiencies FIRST is like the leftist tactic of saying "This nation was founded by slave owners...CASE CLOSED." So we can take turns destroying historical figures for their shortcomings. Or we can say that our country needs heroes. And blacks (and I would add, whites and people of ALL colors) need a good role model. King fits the bill in both cases.