They've knighted him as their hero because the Left has been so inept at arguing that he's not a hero.

The Left should have said this: "Rittenhouse was defending himself, fine. Why did he need to? Did the people he killed deserve the death penalty?! No? Well then this was pretty messed up, wasn't it? This whole "private citizens carry guns into dangerous situations, get in trouble, kill people" is pretty much a disaster, huh? Maybe we ought to fix this?!"

"My hero ineptly got himself into trouble and engaged in the extra-judicial killing of two people!" is too awful of a message for even the Right to rally around.

That this isn't the message is totally on the Left. Because it's entirely true, entirely supportable, doesn't require you to get inside Rittenhouse's soul and examine his motives...it's just a plain statement of what happened and how (%*#$ messed up it is.