Martin Luther King was a Republican. Most major civil rights laws were championed by republicans. During the civil war it was the republicans that were considered the Abolitionists and the ones who supported the right of Blacks to be free from slavery. It would be more accurate to say that the Democratic party has traditionally been the one to fight most of the civil right progress that has occurred in the United States.
The black population has been voting democrat in majority for many years now, and in large, they are still in poverty in relation to many other countries. To say that black republicans are sellouts is false, maybe they are sick of a rotating cycle of poverty after promise. There is definitely an echo chamber of people who say, republicans hate"blacks" or other minorities. This is echoed up to the president so the democratic party can keep votes.
How can a POC republican be a sellout. This is common for Democrats. They c go on and on complaining that the republican party is racist because a majority of their members are white. They say that more POC's should be there and when they discover there are, they call them sellouts. What? Aren't you the ones always complaining and whining about how the republican party needs more ethnic diversity? Oh I see the picture, you actually just don't want there to be any POC republicans because you want them to vote Democrat so you can just use them. Typical of Democrats.