This is a genuine question, not shitposting...mostly.
I do not think he had any businesses being in Kenosha at 17 and not directly defending his life and property. This has nothing to do with the fact he did society a favor in removing three utter dregs, but rather the first rule of self-defense Is to not get yourself in such a situation in the first place. He played stupid games and won stupid prizes. I think it was 100% self-defense and justified. Rather why was he there in the first place as a minor?
He wasn't in Kenosha to help defend stuff. At least not originally. According to his defense (and keeping in mind they have as much an interest in the truth as the prosecution, which is: not much), he was already in town in unrelated business, took the time to help clean graffiti left by rioters on the local high-school, and was asked alongside a friend to help keep what was left of someone's business from being torched in another night of rioting. He was offering medical assistance to anyone who came up,
including rioters, which is why he had those gloves on (some people seem to think he had them on to avoid leaving fingerprints). As with any Roof Korean-adjacent situation of armed people standing in defense of property the intent wasn't to be there to shoot anyone. It was deterrence. In his own words, he was hit with pepper spray and didn't react because no one in his group had non-lethal methods to retaliation.
Now, the answer as to why he was there in the first place as a minor? He was dumb and idealistic. That's teenagers for you. He was trying to help the best way he could think of. On a similar token, I'm pretty sure a lot of the rioters were also minors. And all things considered, Kyle did a lot better than most trained
adults would. He got singled out and separated, and when someone who had been heavily belligerent against him (Mr. Baldyhead "shoot me, nigga!" Chomo), threw at least one object at him, chased him into a dead end and then lunged at him to grab his gun, he fired.
With the immediate threat neutralized, he hung around long enough to make sure the guy was getting medical attention (someone else was already crouched besides Baldy), then left when he realized the crowd was turning on him. He ran away as far he could towards the police to turn himself in, got knocked down, kicked and hit by a skateboard, and fired when someone (Mr. Sk8er boi) reached for his gun again. The third guy (Mr. Bicep) came at him with a pistol, hesitated or pretended to back away, moved in to shoot, then got shot for his trouble. And even after all that, Kyle still moved towards the police with his hands up to turn himself in.
And even after the police told him to keep moving (since they were more worried about the wounded), he turned himself in at his hometown without resistance.
So... yeah. In retrospect, I'll call him foolish for getting into that situation in the first place. But there's no way he deserves even half the criticism he's been getting in media, or even a tenth of the legal action being flung his way. He's a teen, teens do dumb shit. But while Kyle was making the best (the least worst?) out of the bad situation he had put himself in, the three guys who got shot were all in their 20s and had no business attacking
anyone with a gun no matter how righteously angry they were. Particularly Mr. Bicep, who as a felon had
no business having a gun in the first place. All the people involved played stupid games and won stupid prizes.
Edit for an important addendum:
While judging his decision to answer the request to help defend those businesses, try to think of the information Kyle Rittenhouse had available to him at the time. In the past three months, the vast majority of interactions between rioters and armed defenders have been standoffs that
didn't escalate. The rioters notice the very visible armed guards, fling insults at them, and move on to try to find better targets. No one had any reason to expect anything different. That was all the information he had, and that he was going around offering medical attention showed that he didn't expect things to escalate.
The fact that there was a bald belligerent hobbit who was so angry/coked up/suicidal he decided chasing, throwing things at, and charging someone with an AR-15 was a good idea was something no one could predict. If Kyle knew he'd end up having to shoot three guys in order to keep himself alive that night, I'm pretty sure he would have gone back home by nightfall.