And the admins (and myself, for that matter) want to exist without the risk of doing a perp walk because Little Timmy saw a peen.
I'm on an NSFW Lemmy instance. I have multiple NSFW accounts spread over the various platforms, and my single biggest fear is that some shithead kid is going to ignore the giant "18+ only" warnings because they're so MATURE for their age, they're going to find adult content (or worse yet, try and message me and pretend they're over 18 so I don't block them), and one of their relatives find out and call the police. Intentionally done or not, I've seen exactly that scenario play out, ruining the lives of multiple people through no fault of their own.
The Lemmy admins all have to worry about this exact same thing too, except they have to worry about every kid and every NSFW account/community, unless they decide to either play whack-a-mole with the various NSFW instances, or move to default deny federation and only federate with known-SFW communities. And that's on top of the existing CSAM spam concerns that they appear to have only recently gotten under control.
I don't give a single solitary flying fuck about whether children can express themselves equally. They're NOT equal to an adult, because I don't risk jail time by showing off my [REDACTED] to them.