Short answer: it depends on your local and state regulations.
Here in California hunting and gathering are legal only for the game listed than you can take while on scuba or surface supplied air. If it's not listed you can not take it.
Many here in Norcal do hunt on scuba because we're after food more than a sporting event. There are limits and as long as the we are operating within the law we see nothing wrong with harvesting on scuba. Freedivers may see it differently, but their motives are slightly different too. I feel freedivers are way more destructive to a particular area when they have their fish killing competitions when hundreds of applicants go out and the motive is to kill as many fish as possible during a set time frame to win an award. There are no sanctioned scuba spear fishing competitions in my area that I'm aware of.
Scuba divers in my experience only gather what they can eat and tend to boast about it much less. We feel because it is considered less "sporting" we don't do it for sport, we do it for the food. The more effectively we can get the food and get it back home the better. After all, a dead fish is a dead fish, it doesn't really matter how it died.
I only take what I know I can eat within a few weeks because I don't like fish that has been frozen too long and has freezer burn. Plus I don't like to clean fish for hours after I get home so that will limit may take.
Regardless what the diver was wearing when he speared the fish whether on scuba or not, spearfishing still remains the most responsible method of take of all fishing methods.
Don't even get me started on commercial fishing!!