In a way they are like addicts: you love them and want the best for them but you absolutely have to be on your guard for egregious breaches of trust cropping up without warning. Children / teenagers / young adults can be driven by curiosity, peers, and lack of judgment into all kinds of dreadful behavior, and it can come from the least likely ones just as much as the obviously naughty ones.
The best we can do is to warn them in advance, accept that mistakes will be made anyway, and support them in learning from their mistakes. Keep at it for even a short while and you too can experience the shock of how your most charming, academically brilliant, upstanding star pupil is found throwing up a bottle of vodka she just drank!
I don't have them chained up, but I'm also not concerned they are become radicalized, or damaging themselves watching snuff films and goatse.
The parents I’ve seen who give up and make no efforts because they think it’s impossible to perfect control everything don’t have great outcomes. This applies to everything from internet to drinking alcohol and more.
All it takes is the kid wanting to go behind your back, the rest becomes easy for them. The only chance you have is establishing a good relationship with your kid and instilling good values. You can't actually control them online unless you lock down their life like a supermax prison.