Batman the Animated Series had an episode where Bruce Wayne wakes up with no memory of who he is in a forced labor camp. He eventually figures out who he is, escapes, and Batman frees all the enslaved people. Is that the kind of safe for kids material you mean?
Sure, that was a good episode. It's also a super hero cartoon, and while Bruce was the victim in that ep, he wasn't put there for the PCs to rescue as part of the game. He wasn't some disposable NPC whose name the PCs won't remember in a session or two, assuming they ever found out in the first place; nor were we, the watchers, supposed to be enjoying his distress, while players are supposed to
enjoy the game, even when it means freeing slaves. Bruce was going to regain his memories, escape, and catch the bad guys. No matter what, that was going to happen. Even little kids who didn't realize that writer's fiat meant that Batman
couldn't suffer for very long knew that he was the hero and was going to prevail.
Are the PCs in an RPG going to escape? What if they roll really badly. Is the GM going to be the type who has a power trip over enslaved characters? For that matter, are the players even going to want to play as slaves? I don't even mean "are they going to be triggered by this"; I mean "is this a thing that the PCs are going to find interesting?"
Curse of Strahd is still D&D and I still feel like the goalposts are being moved.
No, they're really not. Because different genres are, by definition, different.
Is it or is it not okay to include elements that might trigger someone or are problematic? The answer appears to be yes. I'll grant you that context matters, what's appropriate for D&D might not be appropriate for My Little Pony, but broadly speaking, yes, it's okay for problematic elements to be included in games. Right?
Of course, MLP had a very laissez faire attitude towards mind control--enough of one it put a damper on my enjoyment of the show.
And more importantly, what you're forgetting (both here and when you bring up Batman above) is that TV shows are scripted. Nothing happens in one unless the writers, editors, producers, etc., OK it. There's no PCs to go off the rails or get upset, no GM who's going to go too far or push too many boundaries. The players are active participants, not passive watchers, and are far more immersed in the experience. If people get upset or bored watching a TV show, they can turn it off; it's hard to turn off a game, especially if everyone else seems to be having fun. Social fallacies are a thing.