Bob, I've read a number of your posts and blogs, have PMd you once or twice, and have immense respect for you as a diver and as a mentor to the diving community. I sense from your question and your post that you are either A. seeking a forum to publicly shame this diver, B. seeking support for the steps you have taken, or C. seeking advice on how to stop harvesting from this location. Implicit in your question and post is that you first approached this diver because you believed his actions were inappropriate. I suspect this young man sensed judgment in your engagement with him and responded as, sadly, many young men do, by taunting you and otherwise escalating a confrontation you initiated.
It is difficult to respond as to how I would handle the situation. I grew up around the killing of animals for food and the eating of wild fish and game. I launched a boat from the Don Armini (sp?) boat ramp just down the street many times in the 70s and 80s, long before and during the infancy of the dive area to which you refer (that dinner boat was still there in my early memories). My view of diving this dive site and divers in general from my youth is one of a local resident who resented divers who took parking spaces reserved for the boat ramp and who unnecessarily exposed themselves when suiting up or down. I took the hunter safety course when I was 12 and have had a rifle in my hand since that day. So I grew up on the hunting side of the hunter/photographer divide and I didn't grow up diving so I don't have the wonderful breadth of experience and knowledge you have as a diver in general and as a PNW diver specifically. So, based on my outlook and lack of exposure to diving this particular site, I probably would have slapped him on the back and have tried to get an invitation to dinner.
What I wouldn't have done is instigate what appears to me to be little more than social media bullying over a legal activity that you find objectionable at this site. Frankly, you are probably fortunate: I was once a 20 year old headstrong young Marine and I can easily see someone inviting you down to witness a platoon sized hunt in response to the pressure you brought to bear. If his activities are legal, who is anyone to castigate them?
Having the benefit of distance from this situation, I see a different, win-win resolution that could have been had and might yet be had (although unlikely). This appears to be an opportunity to bring change through education and mentoring. The young man says he wants to become a rescue diver and seems to acknowledge that he could have handled the situation differently. You say you support hunting (just not there) and are clearly in a position to mentor this young man (it seems that he needs a positive role model based on his reported facebook postings). So, my answer to what you should have done (and what you might yet do) is to offer to show this young man a better way (and better place to hunt) and mentor his skills and appreciation for the world under the surface. I know I would give up chocolate and beer for a year for the chance to learn a fraction of what you could impart to this fellow.
R/S,
db