Then I'd say the motive was that Kennedy was getting too soft on Communism, the possible specifics of which have been mentioned about 50
WS: Charles, do you really believe that? Then how do you square it with the fact that JFK scored a really, really big victory in the Cuban Missile Crisis without firing a single shot. Even without knowing what we do today (i.e. that the Russians did have tactical nuclear missiles in Cuba and would have used them if attacked) - having the Russians blink and pull out was a major political and moral victory which overshadowed the Bay of Pigs fiasco.
With that in mind - focus on JFK's assassination obscures rather than elucidates the politics of the Cold War and the US empire in general. The empire does not need a cabal conspiring in their basement to overthrow the will of the people - it operates in a full light of legitimacy and relative openness. The oligarchs are quite open what they are going to do and how, before they actually do it (cf. PG Wars I & II) - they do not need a secret assassination team to pursue their war plans. "Conspiracy" is, in fact, strategic business/political planning done in full day light and as much public scrutiny as any democratic state would allow it.
The JFK's assassination, whether done by the mob, the Cuban mafia or by some right wing fanatic is simply irrelevant to the workings of the empire, just as the assassination attempt on Reagan by a rich psychopath is.
Wojtek