Perhaps...
But supporting civil rights in America - wasn't a demonstration of their righteousness or "humanity", it was a wedge issue they attempted to hammer into a schism in America....
"Civil Rights" and HUMAN RIGHTS were unknown in much of the good ole "Soviet Union" of the big guy -- Joseph Stalin....
One can apply lipstick on a pig -- but on Communist pigs - it doesn't make them anything but a silly looking pig.
Even a broken clock - is correct twice a day...
The Communists couldn't even come close to matching that standard.
Semper Fi
I've known a few communists and they were very nice people, if a bit fixed in their opinions. It isn't necessarily true that communists leap out of bed every morning with a cry of "Evil, I take thee for my good!" although I'm inclined to agree with you that Party support of the civil rights movement was cynical.
The main thing is that MLK had plenty of reasons to act as he did without our imputing dark motives to him. What the communists did they did for their own reasons.
Incidentally, in the military a stopped clock is right only once a day. ;^)