So there is a conspiracy related to no security? (There was, literally, very very little security. But there hadn't been much up until that point, nobody had tried to shoot the President in a 100 years.)
Pretty much NOBODY back then (American citizens, I mean) thought "OMG he should have been in an armored bulletproof car with FBI snipers in every window downtown." That's like my Mom being pissed at Air Traffic Controllers for not "doing something" to stop the terrorist hijackers on Sept 11, even though nobody had ever flown a jumbo jet into a skyscraper, using it as a giant flying bomb full of jet fuel. We learn from our mistakes, hopefully.
The friggin POPE was shot and now has to ride around in the bulletproof Popemobile. But he didn't for many many years.
JFK was warned not to go to San Antonio, but he received these warnings all the time. There were far more American nuts wanting to kill JFK than Russians or Cubans. Lincoln received the same warnings and had the same risks, but the "luck of the draw" (um, no pun intended) is what it is, and that day his luck ran out.
This is interesting, though: http://www.history.com/news/jfk-assa...sified-release <--- warning, there is a graphic photo of the car seat where JFK was killed, ugh
If the Mexican CIA operatives knew of the possibility that Oswald was out to kill Kennedy, the risk existed in every city in America, and what JFK's team should have done was keep him at home if they couldn't keep tabs on Oswald. Unless the Mexican operatives didn't even bother telling the D.C. CIA team. It's more than just a matter of putting security in every building on the parade route; it's putting the President in a friggin' convertible, etc. The whole thing smells like a deliberate operation, which is why we have so many conspiracy theories of the CIA using Oswald -- a person allegedly known by intelligence people as wanting to kill Kennedy -- and putting Oswald in the pawn position to get what they wanted. Allegedly. Also, Oswald insisted - even on national television - that he DID NOT shoot JFK. Then, he never got a trial.
dun dun DUN ...