[Oliver_W]

The child orgy was obviously gross, especially with how much detail he goes into with the anatomical descriptions etc.

That said, it's clear why it happened - the supernatural bond between them had been diminished with ITs defeat, and they needed to rebuild it so they could get out of the sewers, and do so without running into the now completely deranged Henry. So the storybeat is a fair one, but should have been hit in a different way.
The bloodpact they made could maybe have been shuffled around and used instead. It would also have fit with the parts when all the Losers' palms split open - instead of reminding them of their promise, it'd be reminding them of the bond.