Two facts that always seem like conspiracy-defeaters to me are that the conspiracy would have to be predicated on (1) Oswald working in the TSBD and (2) JFK’s motorcade passing in front of the TSBD. It would have to be a last-minute conspiracy, consistent with Oswald's actions on Thursday.
But let’s consider a plausible conspiracy scenario. I gather this is where Hancock and Boylan are going in The Oswald Puzzle, but I still have more than 100 pages to read and am not trying to put words in their mouths.
Let’s say that up until the assassination Oswald’s life is pretty much exactly as Lone Nutters (and I and apparently Hancock and Boylan) believe it to have been. His high-profile activities in New Orleans and Mexico City cause rabid anti-Castro characters who are enraged by the Bay of Pigs to realize that this pro-Castro former Soviet defector is a potential patsy who is almost too good to be true. If they are successful in inducing him to act, not only will JFK be gone but the finger will be pointed at Cuba.
Pick any handful of the anti-Castro usual suspects you like, although I doubt they would include anyone as easily identifiable as rogue CIA operatives. They convince Oswald they are as pro-Castro as he is and that eliminating JFK would make him a hero to the Marxist cause and assure him a warm welcome in Cuba. Perhaps they even promise him safe passage to Cuba.
But they do no more than this. They don’t get their fingers dirty at all. Up to and after the assassination, Oswald has no reason to suspect they were anything other than the rabid Castro types they pretended to be. He thus carries out the assassination.
The subsequent multi-agency cover-up, as Hancock has previously suggested, is more in the vein of CYA activity than anything having to do with the JFKA per se.
Is this a conspiracy? Sure, of sorts. Was Oswald a patsy? Sure, of sorts.
Is this conspiracy meaningfully different from the Lone Nut scenario? A bit – but not much, it seems to me.
Is it more plausible than any of the more grand and elaborate conspiracy theories? Absolutely, it seems to me, although I still have great difficulty accounting for facts (1) and (2) above. It does account for Oswald's silence - he wouldn't have realized he was a patsy at all (his actual "patsy" comment not suggesting in the slightest that he was a patsy in an assassination conspiracy).
Would it satisfy John Armstrong, Jim DiEugenio or any of the others who have made a cottage industry out of grand and elaborate theories? Of course not. Predictably, The Oswald Puzzle seems to have received a very lukewarm response over at The Education Forum.