You can't pre-meditate self-defense. You can go somewhere with the expectation that you'll need to defend yourself, which is dumb, but not a crime. Planning to hurt someone is very different from trying to put yourself into a situation where hurting someone would be justified. The first is a crime, the second is just being stupid.

For example, look at those people who do 1st amendment "audits" who basically go to places where they know the police would be called with the hope that the police will violate their rights (e.g. filming at a police station). That's not a crime, but it's usually a waste of time, but it sometimes provides a valuable service if it creates a situation where bad cops break the law on camera and get held accountable. But whether it provides a valuable service or not isn't particularly relevant here, what's relevant is that it's not a crime.

And that's what happens here. Kyle Rittenhouse is one of my least favorite types of people, but I firmly believe that he was justified in using his firearm in self-defense. That doesn't make him a hero or even a good person (I think he's a terrible person), but it does mean he's not a murderer. Murder is the unlawful killing of another person, and his actions were lawful self-defense.