"Documented violent history with firearms" - ?
You also speak as though "the FBI" were some monolithic entity. "The FBI" in this instance was Hosty. The whole point of people like Shenon is that better intra-agency and inter-agency communication would have at least put Oswald's employment in the TSBD on the SS's radar screen. (It's entirely possible the SS would have been satisfied he was harmless as well. Hindsight is always 20-20.)
Other than the fact that the CIA, FBI and SS dropped the ball, which everyone agrees is true, what is your point?
A suspected russian asset currently under FBI investigation as such ,with a documented history of criminal violence towards authority figures , criminal use of illegal firearms , being considered "harmless" enough to be sitting in a 6th floor snipers nest within spitting distance to the President ?
It takes some king-kong size giblets to own up the failure of 17 experienced FBI agents, the CIA & SS to include in their possible threat list an individual with a documented history of criminal violence towards authority figures , criminal use of illegal firearms , and then call other people "conspiracy theorists "
You do concede there was a threat list of individuals shared between the FBI & SS for the Presidents visit to Dallas, as is standard procedure to this day don't you ? Yes, No