All due respect, you didn't answer the question.
Pyrrhic victories are meaningless. In the end, who actually followed through with change?
Obama himself, the first black President, sympathized with you that change never seems to come quickly enough. Partly because people like Trump are so damaging and disruptive to progress. In their absence, we'd be far more free to advance more quickly. Alas, that's just dreaming.
So in the end, it was those liberals in Congress who passed the monumental change. And without question, MLK had more allies among them than he did the Confederate successors in the KKK, obviously.
In the end, some change is better than no change is better than regression through entropy.
If I was on the left and leaning to not voting because of gripes with Harris on one single issue... I'd certainly rather be dealing with holding accountable the Harris administration over a Trump administration over the next 4 years.
That's leaving aside the fact that it's always easier to break something than maintain or build upon it.
I'd certainly trade one issue where there may be a constant on (there isn't) for wins on a range of other important issues, as well.