If you're letting children browse the internet without supervision, they're going to be the ones who end up needing professional help.
Raising your kid the way you think is right is your job, not society's. If that includes shielding them from horrifying imagery, then shield them, but don't demand society shield everyone because you are too lazy/incompetent/whatever to rear a child properly with the assistance and cooperation of 7 billion other people.
And if you're worried about them seeing these things while outside your influence, might I suggest you do a better job teaching them right from wrong, so you won't have to worry about them getting their morality from YouTube videos.