As stated before, the OP doesn't specifically violate any rules, and the thread devolved on its own by multiple persons with a shared interest. The pictures that were deleted were over the line, this in turn summoned more anons to the thread, which more borderline things were posted.
Borderline images (Grey images) are left up to the staff of each board to decide whether or not they want to delete them; this varies between staff box and year period as taste and people change.
Because you don't like something doesn't mean it is against the rules. You could throw out the "Uhhh fetish is fetish, no exception." but people only believe in that with fetishes they don't like, and never bring it up with fetishes they do like.
"All Vore is Fetish, purge it. Now excuse me, I'm going to make a Fat Pokegirl thread."
The rule of thumb when it comes to grey line images: Vore:
Over emphasis on internal shots is playing with fire, however depends on quality and personal taste of the staff box. Heavy digestion or completion of vore [Essentially Dirty/In Depth Vore] (whether that is scat or belly fat etc) is usually going to get deleted and should be deleted. If you post Hard Vore (blood and guts, chewing) then holy fuck you go back to /b/.
Its kind of like the grey line around Macro/Micro content; There is seemingly innocent stuff, risque stuff, lewd stuff, fetish stuff, okay this is porn stuff, and Holy shit what is wrong with you stuff.
You can't group all of it together (Unless you are a knee jerk reactionary retard) Nor can you tolerate all of it because it would violate board rules.
The Grey line is interesting, and its something that people have to understand when applying for 4chan staff. People who don't understand that should never be staff members, and those are the one that use their powers to launch personal crusades against things that they don't like.