It's called due diligence. The guy had a conviction on the record for underage prostitution. This isn't mom and pop's corner gas station, this is MIT, a well respected institution. You don't get "well I had no idea this man who has a public criminal record had a bad history" when MIT is running background checks on janitors that wouldn't get through with something like that on their record.
The world needs more accountability, not less, especially amongst those in power. Patting this guy on the back for posting an apology on the internet is effectively approving of the status quo that got us here. MIT can and should do better.