I agree, in principle vigilantism isn't good for society. It opens the door for, let's say heavily misguided, people to carry out whatever justice they want. Yes, it is also dangerous for the individuals with good intentions.

However, if the "proper" system does nothing, who will?

In the case of Roblox, I'm going to compare this to a public park;

In this park some adults set up a free candy van for kids. The park rangers/owners (moderators) see this, and choose to ignore it. Some other people at the park report their concerns to the rangers, yet a week later they find 3 more vans have shown up.

Finally, one person steps up and calls the police directly. The police can do nothing with the information, as there's "no evidence". Desperate to stop them, the person disguises them self as a child (don't ask) to get the evidence. Police show up and apprehend the perpetrators.

The rangers are now angry that the person called the cops to their park, and bans that person from the park for "pretending to be a kid".

If Roblox is unwilling to participate in the justice system set by society, they have no place in it.

As for schelps making YT videos, I say keep doing it. Not only does is help spread awareness to issues like this, it documents the "vigilante" actions. Society can decide from there what to do with that information.