Yes, our prisons should be safe for those who are confined within them. I agree with that, and that less people should be confined in the first place.
But there is a qualitative difference between "he was stabbed due to being a cop (or due to being THAT cop)" vs "He got into an altercation that resulted in him being stabbed, but which could have happened to anyone."
I think the kneejerk assumption is that he was targeted, which is worse IMO.
Not that I shed a single tear for the fate of Derek Chauvin, mind you.