I think a parent should have a pretty good idea about what their kid gets up to on the Internet; I know I would if I lived with my daughters. At the same time, I know that the more trust and respect you show a kid, the more they open up to you.
If they know that they can talk about anything with you, they have the biggest protection you could desire for.
My 12 year old daughter told me recently she'd tried a cigarette. I know she'd never tell her mother, but she felt safe telling me. I was fine, as she'd tried it, didn't like it, and had told me. It meant I could talk to her about the whole topic of drugs in a very open fashion.
At the same time, I think unless there is something pretty clearly inappropriate happening, to jump in and judge another parent's wisdom before having even ascertained what the facts are is dumb. I wonder what the reaction of people who do that would be if someone who hadn't checked their facts told THEM they weren't looking after their kids properly, or implied it, in a public area.
I also think parents kid themselves. Having an open relationship with my daughters mean that I know what happens at school. It is not a Methodist picnic. Kids are rude and crude and always have been. Adults have always pretended otherwise.
I prefer not to maintain this pretense. I can share in a disapproving conversation my daughter instigates about a girl in her class who she thinks has 'done it', and it's GREAT. A relaxed conversation where I can make sure she knows that her friend might just be lying, as people do, that it's far too young if it is true, and why, about the risks, and learn that she likes boys but find the idea of sex physically repulsive (her exact phrase was (complete with theatriucal shudder) "I don't want a boys stuff up inside me"). I get to tell her that's NATURAL to feel that sex is icky at her age, but that it might change in a half-dozen years or so (she was skeptical over this!). Hell, I love being so close to my daughter she can talk to me about not starting her periods yet and how she feels about the eventuality.
She needs it as she's being raised by an over-protective, over-reactive, nominal JW who doesn't attend meetings but is still in mental thrall to the Borg. I never could have a normal conversation with that woman, I don't see how my daughter could! 8-).
I digress. Jumping on another parent's actions without facts is dumb. Expecting a web-site to act en loco parentis is dumb. Thinking that pre-teen kids live in a sanitised world is dumb.
You cannot srap trainer wheels to your kid and let them peddle off, expecting them, when they rip 'em off themselves, to be able to ride. If you do that, they'll fall off.
You cannot stick a kid on the back of a tandem, and then expect them to be able to ride a normal bike just by following your example. If you do that, they'll fall off.
You have to take the trainer wheels off and run with them guiding and stabilising them until they realise they can do it themselves. If they get a little ahead of you and fall whilst they're learning, you're close enough to help, but not to close to intefere with them growing up.