The Left never should have been demonizing Rittenhouse in the first place. Unless we stopped believing in the rule of law and instead believed in the rule of what people can be coaxed to feel is right without understanding the details, he was going to get off.
The Left had a perfect opportunity. Yes, Rittenhouse is innocent. He also blundered into a deadly situation with the stated intent to do good, armed to protect himself but without the training and coordination to actually make it safe. This resulted in two extra-judicial killings, one serious injury, and grave danger to his own life (in large part because of guns owned by people threatening him, in addition to the deaths of the people he killed--there were three guns relevant here, only one of which was Rittenhouse's). This shows the critical importance of (1) stronger gun laws, (2) good public services (including national guard as appropriate to prevent destruction during riots, and fast effective compensation for property damage so it's easier to stand back and let a violent mob destroy some stuff which is just stuff and not have to make the tradeoff between stuff and lives), (3) recognizing how badly things go when people take justice into their own hands even if they end up only committing legal actions--for instance, our justice system would NOT have sentenced Huber to death, without trial, for clubbing someone with a skateboard, and (4) having better laws regarding individual actions endangering public safety to dissuade this kind of action in the first place.
But, no, instead of showing how the standard Democratic viewpoint was proved correct with flying colors here, the Left had to make out Rittenhouse as some sort of monster stalking the streets of Kenosha looking for victims to murder, leaving all the entirely sensible criticisms and commentary on the floor, the Right in control of the narrative, and ending up with a judicial "defeat". And making stupid not-even-argument arguments like "he traveled across state lines"...who even cares?! People travel across state lines for BLM protests and other efforts for justice, or to help in natural disasters, and that's a good thing!
It is really insane. One could hardly do worse if one tried. I wouldn't think even a rather devious Republican strategist like Bannon could have devised a big of a fail as the Left concocted for itself. But, of course, the Right has gleefully made the most of the Left's faceplant on this.
Really, really super dumb. Not something to get all worked up about, either, because the narrative was based largely on misinformation and ideology, and the point of the justice system is to ignore all that crap and focus on what actually happened and what the laws actually were. And guess what? That's mostly what happened. And Biden sort of acknowledged that the justice system was working how it's supposed to, which is totally fair. AND because the Left wasn't on top of a reasonable, reality-based narrative of what happened, it's probably lost most of the initiative to fix the laws in Wisconsin to make this less likely to happen.
The situation with Arbery is totally different. If the murderers aren't convicted of murder, something is deeply wrong (and Georgia realized already that its laws were encouraging this kind of deep wrongness and it already changed them!). The only possible question would be whether it's first-degree or second-degree murder, except Georgia doesn't recognize distinctions between types of murder. Indeed, the Rittenhouse verdict suggests that if Arbery had gotten the gun of one of the three violent aggressors who were assaulting him, and had shot and killed all three, he would have gotten off on self defense. Of course we know that things tend not to actually work that way in this country, but they sometimes do, and regardless, that's still the message. If we make that the message, it's more likely to go that way in the future.