My guess is that it would prevent some, but not all, of that.
That's okay. My analogy is the way we handle magazines. If I had a copy of Penthouse at home I wouldn't leave it in the living room where my 8 year old could find it. I'd probably keep it under our bed or in a draw in my bed room. Is it possible my child could stumble accross it ? Yes. If he can stumble accross it should that mean I shouldn't take reasonable steps to block access ? Of course not.
Is using software that adults can bypass the equivalent of putting the magazine in your sock draw ? Yes. Should we just leave it out on the coffee table because we know they will get it anyways or because some guest might want to read it ? Sorry, no.
I owe it my children to help them avoid what they would consider "gross" and what they are not ready to deal with yet.
You can say that about anything. Should we legalize murder and rape because we can't prevent all of it?