Lots of points to respond to:
(1) I believe that I've spoken with Mr. Magnolia on two occasions -- he spoke in a soft tone and did not beat his chest, so to speak. Any speculation that he's going to go postal is a bit over the line.
(2) When I spoke with him, he said that I was on private property; he asked me to leave. I was pretty confused at the time, since I was standing in front of the street, not his house. I remember telling him that it didn't even occur to me that the land was privately owned, and that I had no intention of trespassing on his land. I told him I would continue to stay below the street. We didn't debate his property lines, etc. I just politely ended the conversation and continued my trek to the rocks.
(3) On another day, I spoke to him again as I was coming off the beach. He has just told some other divers the same thing as in (1). I approached him and asked why he was even upset with the divers. In my limited experience, the divers show up, put gear on, and dive. I didn't see any picnics, etc. I was trying to figure out what this guy's beef was. He said that he didn't have too much of a problem with the small groups of divers, but that he didn't like the shops (and presumably, the clubs) bringing large groups of people to the site. I don't remember him mentioning anything about trash or noise. In fact, I don't think I've ever seen any trash there.
(4) This issue will never be settled until someone figures out whether the access path is on his land -- he may very well have a point! Maybe it's possible to make another path at the bottom of the street? Next, we need to figure out how far his land extends to the water. It's possible that he owns to the low water mark (the general rule), but it's also possible that the original grant of the land didn't include it (the exception). Once we figure that out, the use of the land between the high and low water marks is the next hurdle. From what I've read, any sort of fishing (e.g. lobstering) would likely be protected in this area. I'm not sure if the act of fishing would include e.g. setting up gear, surface intervals, etc. Maybe people could simply gear up on the rocks beneath the street to avoid any problems? These aren't difficult questions to resolve -- the hardest part is the title search.
(5) Even assuming the worst case scenario (he owns it all), my guess is that his main beef has nothing to do with a few divers crossing the path or sitting on the rocks for an hour on a Saturday morning. I think he's just pissed about the cars parked and the divers changing. Keep in mind -- you're basically parking in his backyard! I do have some sympathy for this. I would hope that divers aren't pissing in his lawn. I would hope that divers aren't changing right in the middle of the street. But I'll bet it happens. You can minimize this a bit -- maybe try to get others to keep a lower profile? But if people are going to dive there, you're going to see them putting on a wetsuit and getting gear ready in the street. Assuming this is the main beef, I'm at a loss as to a solution or a compromise.
(6) I'm with those that want to resolve this by talking to Mr. Magnolia and/or his lawyer. While I don't agree with his approach (i.e. RICO actions!) and I don't understand why he wants to spend a Saturday confronting divers, I do think that he has a legitimate point as to the nuisance (changing divers in his yard) and potentially a legal right as to the access path. I don't think anyone should antagonize him for any reason. If that's where you want to dive on a given day, knock yourself out. Maybe just try to stay below the street? Also, I have no idea whether the multi-club event was planned there just to spite him (I assume it wasn't), but the perception will be that it was.
(7) Finally, i suspect that at least some people on here have a tendency to assume he's wrong or a jerk just because of where he lives. I agree that he doesn't own the ocean and should expect some nuisance (e.g. people walking along the rocks at night) that goes along "with the territory." But let's not spite him just because he lives where we'd all die to live. If my backyard abutted two streets and I had to see a bunch of chubby guys (myself included) squeezing into stinky wetsuits while I read the paper on a Saturday, I wouldn't like it either. Let's try to be fair about all of this.
OK, it's time to get off my soapbox...