Here's a thought exercise for you:
-- JFK, through his brother RFK, was threatening the very existence of several powerful Mafia organizations, especially those of Marcello and Giancana.
-- JFK allowed RFK to humiliate Carlos Marcello by (arguably illegally) deporting him without due process and leaving him stranded in Guatemala.
-- Thus, certain Mafia leaders had powerful motives for wanting JFK dead: revenge and survival.
-- Some Mafia leaders were overheard talking about killing JFK before the assassination.
-- A credible informant reported that Marcello admitted being involved in JFK's death.
In contrast,
-- Oswald had no known motive for killing JFK, and he adamantly denied killing JFK at every opportunity while in police custody.
-- By all accounts, Oswald admired and thought highly of JFK.
-- According to the lone-gunman theory, Oswald tried to kill General Edwin Walker, a fanatical right-winger. It boggles the mind to imagine why someone who wanted General Walker dead would feel any desire to kill JFK, given that JFK had criticized and publicly humiliated Walker, and given that Walker had accused JFK of being a traitor.
Well, no thread stays on track for more than four posts on any forum, so I suppose this was inevitable. My point was not to launch a discussion of the Mafia scenario. I just chose it as a "What if?" example.
You're not telling me anything I don't know, which is why I find the Marcello scenario the most plausible CT scenario. The Mafia, which had assisted Joe Kennedy in the election of JFK, felt betrayed by RFK's zeal for organized-crime busting. Not what they had anticipated. Marcello was personally humiliated by RFK. Those things in themselves are sufficient motive for what would have been a routine hit, notwithstanding that the target was the POTUS. While I don't think LBJ was quite the fiend he is often portrayed as being, surely he would have been expected to be far more Mafia-friendly. If we then add the bonus of the possibility of a made-to-order pro-Castro patsy triggering an invasion of Cuba, thereby opening the door to the restoration of the Mafia's lucrative Cuban empire - well, it's perfect, almost too good not to be true. Marcello would not have needed or wanted the CIA, DPD or any such nonsense. This would have been a tight, closed operation, absolutely a routine hit with zero risk even if Oswald were caught and revealed all about the pro-Castro operation he thought he was involved in.
Probably this didn't happen - but it's the most plausible CT scenario by far. The elaborate scenarios where the Mafia is in cooperation with the CIA and whatnot, and all sorts of elaborate plans and cover-ups become necessary, are simply silly. Marcello would have laughed at any such scenario. (Yes, I know about the relationship between the CIA and Mafia, but Marcello would not have been this stupid when it came to offing the POTUS. A Marcello operation would have been tight and controlled with absolutely no fingerprints left behind and no need for anything resembling a cover-up. Idiot Oswald would have been the built-in cover-up.)
No motive on the part of Oswald? As long as he thought he was involved in a pro-Castro operation, he had a very strong motive. Gus Russo has, I believe, established how well-known in the Cuban community (both pro- and anti-Castro) JFK's and RFK's personal vendetta against Castro was and how imminent were their plans to rid themselves of him once and for all. Castro's own warning about assassination attempts was widely published just a couple of weeks before Oswald went to Mexico City. I always felt Oswald had sufficient motive (complex as it may have been) before reading Russo, but Russo's work has given me great confidence that Oswald had PLENTY of pro-Castro motive, either as a LN or as part of what he thought was a pro-Castro conspiracy. There is no way that on 11-22-63 Oswald still "thought highly" of JFK if he ever did.
Your Walker stuff goes nowhere. Oswald had strong civil rights sensibilities as well as Marxist ones, and Walker was an entirely plausible target when the shot was taken. JFK was an entirely plausible target for pro-Castro reasons when those shots were taken 7+ months later. JFK's and RFK's known anti-Castro plotting would have rendered JFK's actions against Walker completely irrelevant to Oswald. By 11-22-63, all Oswald cared about was Castro and Cuba.