Not even close to being comparable, imo.
Ali refused to join a war which we know now was a war we should have never been fighting in - and had intelligent, logical reasons for his refusal. Ali was able to vocalize his innovative ideas which generated discussion (ie heated debates) then and those ideas are still used today.
While Ali was protesting a true national policy (a war), Kaep is protesting isolated incidents.
Even if Kaep somehow starts a movement with this silly thing - what's going to change? How can one change natural occurrences within a society and actions from individuals by protesting a country's flag and anthem? Even if one thinks the flag symbolizes government polices - there's no U.S. policy that calls for the mistreatment of black people.
Monumental differences between the two.