Problem is I've read reports that Japan has a pretty huge unreported sexual harassment issue with minors. Though a lot of that is apparently due to their shame culture.

The whole schoolgirl getting groped on the train thing is a trope for a reason.

But as I'm far from an expert and only recalling things I've read, google throws up some corroborating sources, but I have no idea on their accuracy, but here is one

But the fact that Japan has had to put steps in place to protect school girls from men who've been taught it is somehow okay to do that kind of thing because their fiction is filled with it is the bit that worries me.

I don't think it is the slippery slope argument as I'm not talking about an endless sliding downfall, just one logical next step - that mass access to realistic 3D animate CP will desensitise people to child sexualization and objectification.
I'm not saying that it will suddenly legalize child brides, or cause massive spikes in rape.
Just that it will shift our already hyper sexualized culture to be acceptable for even younger girls - though that is happening anyway - especially in the US.

Sorry but the idea of seeing young girls pole dancing as part of beauty pageants worries me as a man with a daughter a few months from being born.

Oh and as a small anecdotal counter point, my best friend growing up was young, but him kissing or being publicly affectionate with his boyfriend used to make me super uncomfortable, the way I got over that... I watched a few hours of videos of men kissing.
Grossed me out at first, but then I got over it - I desensitised myself to something I once thought as gross.
3 months later (at 16) I was drinking with him in a gay bar and not giving a stuff about men making out, despite having zero inclination to homosexuality myself.

I did that because my rational brain said "nothing is wrong with homosexuality, after all my best friend is gay", but my herero monkey brain still wasn't willing to concede that.