OMG. Martin Luther King, Jr., was and is a major influence in the lives of people of color, and if you haven't noticed our athletic teams include such people of color. What, come play for us, come entertain us, come suffer injury (and insult for us), but by goodness, leave your heroes and ideas out of…what, MY ARENA? And if you listen to just King's words, we should all probably try to live by many of them, as well, as they line up with many Biblical principals. King was a preacher before all else. Was he perfect in his conduct in his personal life? Not always. But that hasn't stopped many of us from following other imperfect preachers, Christian artists, and Christian authors, because we know no one IS perfect.
If espousing kindness and Justice and equality is political, then Jesus was head of state. NOTHING on that shirt espoused a political party, a candidate or a political stance unless you support a party that embraces cruelty, injustice or inequality. Hopefully, that's not so.