It’s not just that he was using one of those scary black rifles that the left hates, though that’s certainly part of it. It’s not just that he killed a few of the DNC’s Brownshirts, though that’s also certainly part of it. No, the real reason that both leftists and RINOs hate Kyle Rittenhouse is that he’s a living reminder of their weakness. In being strong and standing up for what is right he reminded them of how a real man behaves and they just can’t handle it.

Why They Hate Kyle Rittenhouse
By Gen Z Conservative

And that’s why they hate him. Despite their preening, despite their attacks on aesthetics and beauty, despite their attempts to erase the past, deep down they know that a male that can’t defend himself isn’t really a man. And Rittenhouse’s existence as a young man that successfully defended himself from multiple attackers reminds them that they can’t defend themselves, and thus aren’t really men.