There's no law making creepy comments like these illegal, at least not in the US. (I can't speak for other countries, and US law is what's relevant here.)
This is an extremely dangerous tendency we have as a society, to throw out the concepts of freedom and due process and justice when children are involved. There's 0 reason to "investigate" someone that leaves a pervy comment on a kid's video, and they're free to have whatever fantasies they want. Anything coming close to investigating someone for something like that is too close to the thought police and sounds like 3rd world Big Brother crap.
A Google search was not sufficient in that case. The guy's employer tipped them off after firing him - it wasn't some sort of automated keyword monitoring at Google.
The search alone wasn't sufficient, but was enough to start it all. In YouTube's cases, there are plenty of comments that demonstrate someone is a sexual predator. In my view, if someone "tipped them off", it would be the exact same scenario.
"A random person on the internet is posting creepy comments" is likely not probable cause, especially as you'd have to convince someone national like the FBI to care without a specific location.
"Someone I know personally is posting creepy comments, and I've always gotten a bad vibe about their interactions with kids" is probably enough to get local cops interested enough to knock on a door.
I hope not. Unless there is evidence of a crime that has occurred or evidence that a crime is planned, they have no business (constitutionally) bothering a citizen based on that kind of tip. This is how lives are ruined when there are no victims.
The former is an ill person; the latter a criminal. Your call for no tolerance for anyone with a certain disease, no matter whether they know it's unacceptable and can cope with suppressing it, is a little too broad in my opinion.
