Well either JF thought he was invisible ,thought he was liked by everyone or thought flaunting a dare would prove something. (with jackie in the car the last one seems irresponsible)

I agree that things may well have changed security wise since (lessons learnt) but its quite popular (shooting presidents) in the states I believe so all in all you can say (no conspiracy) he almost brought it on himself.

On the conspiracy its as cd says you cannot find hard evidence that anything that happened wasn't as told,except of course ''was it plotted in advance''