I agree, the average situation is certainly rife with more nuance. For example, my young ones play Minecraft, despite that being implicated as a vector used by pedophiles to find and groom victims. However, I long ago did like you have suggested and limited the online options and communications my kids can interact with, as well as using that as an opportunity to speak with them about why those protections where in place.

My issue with Roblox is that as a company, they routinely downplay the role their platform plays in such crimes, and have actively prevented such activity from being stopped while taking no steps to filter or moderate such things from their end. Yes, parents need to do more then just hand a child a screen so they stop needing attention, but a platform that exploits predator usage is exploiting children.

Now some parents may not be knowledgeable about this, and I can understand that "you don't know what you don't know". However, a parent who chooses to sour a family holiday because the whim of their spawn was not bowed to is not, generally speaking, a good parent. The combination of this with the usage of a pedophile-supporting platform aimed at children while clearly not setting healthy boundaries with the child, are the reason I would say this person is a bad parent. It's not one factor, its the culmination of multiple that result in this reasoning.