Btw, even if 'cc boundaries' were a good idea and in theory ought to be enforced, in practice that is an incredibly dangerous environment to create.
Let's think this through. If you tell your fandom to police what other fans make and inform you if someone is breaking your boundaries... and the main topics you ban are gore/sex/'mature' content... and a fairly large subset of your fans are teenagers/children....
what do you think is going to happen?
The answer is an army of children harrassing people on your behalf, while constantly exposing themselves to smut & gore. They will then either write callout posts to try to punish the creators (often reading/examining the content in-depth to do so) or sending the porn/gore/mature content directly to you (or older fans with more social clout who loudly proclaim their dedication to this fight¹) to deal with, in the name of protecting their fave.
To be clear, I have seen this happen before in other fandom contexts, it is not a theoretical outcome. And it is FAR far more dangerous than any story someone could write and post on AO3, or any art posted to Twitter.
This is an environment that will get kids/teenagers hurt, regardless of intention. It's the underpinning of why I'm so vehement about freedom of speech and creativity within fandom, because no matter what intentions are, the reality is that 'cc boundaries' create an environment that is extremely hospitable to abusers.
¹ Even if your intentions are pure as the driven snow, some of the adults who campaign vehemently for enforcing boundaries will inevitably be doing so because they are creeps who like exposing kids to nsfw content. The cleverer predators privately convince kids to RP/write/draw 'boundary breaking' content, which is then used as blackmail to ensure secrecy or else risk ostracization if they went public with the abuse. This is not a hypothetical.
