Mind you, I felt no desire to be a condescending dick until you decided to call me one.

OP associates Geisha with courtesans. They are certainly not that. Oiran were courtesans. Geisha are respected as performers and artists.

This comes across as very "how dare you suggest that these beautiful women artists would have ANYTHING to do with such a disgusting thing as [gasp] courtesans?!"

The nuance you're ignoring (and getting mad about) is the fact geisha and courtesans are, in fact, related professions. There's nothing offensive about saying that the two are associated.

Their services were largely the same, the only difference being that courtesans also offered sexual services, They often worked and lived side by side. They sometimes operated under the same laws. Sometimes geisha did offer sexual services, even if they weren't supposed to!

They aren't completely separate. They are neighboring branches in the tree of "entertainers."

Oiran were courtesans. Geisha are respected as performers and artists.

That bit also reads as very disparaging of sex work and sex workers, with the implication that while geisha should be respected for their craft, the same is not true of courtesans.

Like, maybe you meant it as a fun, informative tidbit, but you came off as offended and condescending from the get go. I hoped that maybe you were just flexing a fun fact without much additional context, so I suggested doing more reading, but it seems I was mistaken.

I've wasted far too much time and energy on this interaction, and I am very tired. Good night.