See, here is the thing; conspiracies are quite often valid in that one happened but mostly wrong in WHY.
There was a conspiracy regarding JFK and it was a cover your ass conspiracy because it wouldn't do for the shee...err...the public to know the FBI had checked out Oswald and declared him a non threat. So, the answer? The Warren Commission came up with the separation between CIA and FBI. They can't talk thus it can't be one or the others fault if something gets missed. What could EVER gone wrong with that plan?
So, 9/11, we already know that the FBI was onto Atta company in plenty of time to have stopped it but, Gorelick and her memo put a stop to that. However, I do NOT believe that that was the end of it. I do not believe FBI and CIA just said "OK", packed up shop and forgot about it. I believe they continued to do what they could and may have even had increased warnings and fears as the fateful day approached but, knowing how bureaucracies tend to work, it had been addressed, sit down, shut up, and hope for the best.
I believe in my heart more than a few people sat in front of their TV's on 9/11 devastated at what they were watching knowing a good bit more about the details than we will ever be allowed to know and stuck, wanting to serve their nation and being prohibited from doing more.
There are all sorts of interesting thoughts that come to mind as to why Jamie Gorelick, of all people, was on the 9/11 Commission. She was there to protect the system. Not the truth.
And that is a conspiracy that has nothing to do with being an 'inside' job.