In order to believe Oswald didn't shoot JFK one has to believe in some pretty strange happenings including some incredibly bad luck on his part, some incredibly fortuitous luck on the part of the conspirators, and a nearly unlimited capability of the people who framed him, killed JFK, and then kept it all quiet for all of these years.
You have to believe in part that all of the eyewitnesses lied or were coerced or were wrong, all of the evidence - forensic, ballistic, fingerprint, handwriting, photographic - is wrong or corrupt and that alternative explanations on what happened somehow are not only possible but were carried out. And then kept quiet.
We can add the element of time: time is, after all, the chief enemy of conspiracies because over time the acts are revealed, people talk, evidence is found; but time is also paradoxically the enemy of conspiracy theories because over time the acts aren't revealed and people don't talk: a negative is essentially proven. Evidence that should show the conspiracy is not discovered.
As Robert Oswald said about the assassination, asking questions is good, raising doubt is fine, but after the tenth time, the twentieth, it's enough: Lee Harvey Oswald shot JFK.