Luckily, you would have a hard time to mark something as off limits on the net.

You can censor the prevalence of something on a specific platform, but users will always be able to link to any content, if they choose to do so.

You would also fail to make the internet safe for children. I know, children do stink, but they are probably better at locating information they are looking for than their parents. Only direct parenting can help here because there is no feasible technical solution.

So we could draw lines all day and it wouldn't really matter anyway.