Is it bizarre? Sure. Is it pornographic or obscene? No, I can't say it is.
It is, in fact, both of those things.
Look: I have defended the scene from a mechanical point of view, and suggested that it's so critical to the plot that the "It" of the title is not referring to the monster at all, but to sex and the transition from childhood to adulthood via sexual awareness. None of this excuses the gross excesses of the scene or the totally unnecessary details (did we need to know Ben has the biggest dick?) or King, as is so typical of his writing, falling into hammer-on-the head literalism because he's usually incapable of a more deft touch. Add to this the fact he was snorting the GDP of a South American country and we can assume he was, optimistically, not entirely in his right mind when he wrote this. By the 1980s King was already fairly immune to editors; otherwise, there is no way this doesn't get cut. King was and is not Samuel Delany writing Hogg specifically to mess with the normies; he was a potboiler, airport bookstore stalwart who appealed to one of the biggest swaths of average readers in all of American literature. Killing a kid in Cujo was shocking;
child sex scenes are something altogether different. Some of the most open-minded, apolitical horror fans I know were appalled by that scene. Not disturbed, not unsettled, not sent to a dark place to reflect on the vagaries of human nature ... just fucking grossed out. Because it is a gross, utterly wrongheaded scene.
Nobody remotely cared about this scene back when the novel came out or when it was made into a TV series or film.
No one has been insane enough to adapt this scene into tv or film, and when news broke of a new adaptation there were plenty of articles talking about "that unfilmable scene" near the climax.
Do people who hate King's politics and his Twitter bloviating opportunistically attack him with this scene? Sure. Is King a pedophile? Probably not, though given the multiple occasions he's used child molestation as a plot point I would be unsurprised to find out he suffers from some trauma of his own. (And I only say "probably not" because you just never know with celebrities; I don't think anyone expected the dad from 7th Heaven aka Commander Decker from Star Trek to be a kiddy diddler.) Is the scene defensible? I think that's a much more difficult question to answer than you suggest.