Stupid People and other not so bright institutions.

That's revisionist history. He switched parties because he was consistently anti-slavery.

He deserves more credit for his pre-Civil War politics as Speaker of the House and Governor of Massachusetts. Yes, he should never have been appointed general, having absolutely no military background; it was an odd political appointment, but there is more to him than his inept military service.

And at least he was for the right cause.
He switched parties because he was consistently anti-slavery.

While history shows he was always anti-slavery he made the part he really got into it because it was politically a good move for him.

There are also some very not PC things about him during reconstruction such as requiring freed slaves to sign one-year employment contracts and requiring them to also work for no pay for public works projects.
You can erase history, remove monuments, and try to rename parks/ bridges et. al. Doesn't change the history of this great country.
In other words, the removal of present-day monuments doesn't change the fact that these things happened and simply allows people to not be confronted by an ongoing idolization (by some) of the perpetrators.