Both of the men Rittenhouse killed were unarmed.
I accept that every shot Rittenhouse fired fell within the framework of self-defence under the law. I also accept that he did have a legal right to be in Kenosha.
Whether he had a legal right to be carrying the gun or not is a little more contentious. Although his possession of the gun was in line with the letter of the law, it seems likely from the wording that the exception was intended to apply to minors hunting and is poorly written, rather than an intentional decision to allow 17 year olds to carry AR-15s. Poorly worded laws are read in favour of the defence, which is why the gun charge was dropped. He likely would not have been allowed to buy or possess the gun in his home state.
But whatever the legality, I don't think it's right that a guy can go tooled up to another city, kill two unarmed people, and pose for celebratory photos with white supremacists afterwards.
The flow of information today is too fast to wait for definitive, legal judgements on every case, and balancing free speech, opinion, and commentary against spreading false news and inciting hatred is an incredibly challenging task. In the aftermath of the shooting, it seems Facebook implemented their 'mass shooting' playbook, which is, from my perspective, completely reasonable.
Facebook choosing not to allow praise or support for a killer is, in my opinion, sensible and logical. Once it became clear that the killings were not illegal, then Facebook removed these restrictions. I'm not exactly an ardent defender of Facebook's policies, but in this case, especially given that none of the facts are in contention, I think Facebook did the right thing.