I'm in the anti-ban camp because restricting access to knowledge due to arbitrary lines like age is the opposite of learning. It is up to the reader and their mentors to guide their reading depending on ability and maturity as needed. No two people will have the same levels at the same age so books appropriate for one may not be appropriate for another.
That said, to nitpick a tad: pointing to the Internet when on a discussion of book banning or restrictions is more "red herring" or "false equivalence" than strawman.
If they bring home fifty shades, I'll treat it just as if they brought in Dean Koontz or a copy of Grendel. I'd have a frank discussion about how not all books and writers are good. They can read it as examples of either what not to do or as warning signs to look out for, either in literature in general or in people's actions. I'd also recommend better stories that they'll enjoy more. If they bring home books I do enjoy but have either problematic contents or authors, I'll treat it just the same. I love Asimov but the way he wrote women was gratuitously sexist. Lovecraft was xenophobic. Rowling is a terf and her house elves and goblins are definitely not good. Etc etc etc
And advise that they may get in trouble if they read it in front of some people because they have this weird hangup about preventing children from recognizing toxic relationships or the realities of the world.
If they're old enough to understand the words and concepts in the book, it doesn't do them any good to pretend like they don't exist.
Again, withholding knowledge and understanding because people think the children must be protected reduces their own agency and tools to understand the world.