I agree with you, but those posting are (I hope) posting it in the mind of a 13 year old boy.......a large proportion of which at that age are thinking about virtually nothing else than how they are going to get their end away (wasn’t just me was it ?) and it’s the ‘wish that happened to me’ response. If it’s offered on a plate, a lot of 13 yo are very likely accept, and keep going back for more because at 13 they aren’t going to have developed the moral compass or maturity to realise it’s very wrong.
The adult, on the other hand, absolutely knows it’s utterly wrong, and to compound things is in a position of immense trust in relation to a minor, so it’s unforgivable.
So to your point, if my 4th year art teacher had offered it up I’d probably still have a grin on my face now, but my parents would have been horrified. I’d feel the same if it happened to my kids.
O/T: Just wanted to add another point (for those of us who recognise the difference between a child's views and an adult's): This case proves that there is a very good reason why we don't let 13 year olds make decisions that could have a profound emotional effect on the rest of their lives. Something that the Trans lobby could perhaps occasionally bear in mind. #justsayin