Roblox is very active in monitoring, moderating, and reporting that sort of activity. Last year they reported 13,316 incidents of suspected pedos/groomers to NCMEC and law enforcement. Can they do better? Absolutely. But Roblox is a massive global platform with tens of millions of children on it every day. And you know where pedos hang out? Places with kids.
In terms of the other questionable stuff (inappropriate, offensive, racist, and generally hateful stuff) I mean it's again a platform inhabited by edgy kids and teenagers. I'm not very concerned about that content. Roblox does moderate and ban users and content all the time. Beyond that? It's on parents to restrict if they don't want their kids exposed to the reality of people, especially kids, being assholes on the internet. [2]
There should at least be a call for law enforcement investigation.