why do they trash threads that have porn in them when they can just block out a single post?

It's just how the system works

This post was edited by Austin on Jul 12 2011 06:56pm

that makes no sense there is a reason?

If a thread has the first post that needs to be trashed the whole topic is trashed. Other wise it would be a topic saying only Inappropriate content.

it varies depending on what it was

sometimes quotes are missed as well from the "bad" content

thus its faster to Trash and not allow normal users to view it