For every one of these pieces of evidence "proving" Oswald couldn't have done it alone, I've seen ten showing he could.
The JFK assassination conspiracy thing is like an article of religious faith--forget the proof, some people "just know" it was a conspiracy.
No, not kidding. I do remember the day/event of his death. I do recall the video (film) of a guy demonstrating how the rifle worked and trying to put rounds on a target in the same time frame, same range. The ‘sharpshooter’ couldn’t do it. As I recall, the story was more about amazement of how Oswald could have managed to do it as an untrained shooter, not so much as a conspiracy thing. Honestly I don’t even remember now if the rifle had iron sights (I think it did) or a scope. I just remember the perception of the moment — that maybe it wasn’t him with that rifle. I don’t really participate in the whole who shot Kennedy thing. I also have probably more doubts than beliefs that Oswald was a lone nut who got lucky. But I can move on ;-)
In that vein I read an opinion piece recently and opined that conspiracy theories exist because as humans we don't like the idea that a single pathetic loser like Oswald or Sirhan can have such a impact.
I think that's a good point.
When you have to explain away the testimony of 180 witnesses, conclusions to the contrary will always be suspect. Same with TWA 800. If it was one or two witnesses, that would be a bit different.