I dunno what would make them unsporting. Spearing while free diving, there are no bubbles. So if the notion is that bubbles spook the fish, it would seem that hunting on scuba would be more sporting than when free diving.
I have done & do both. With many fish not much matters, they're just plumb stupid. With others, bubbles or lack of bubbles means nothing. body language, hand movement & such matters far more. Let a grouper turn & hit you with with his lateral line when you make a sudden move with your hand & that puppy is out of there right now.
FL state law says they're illegal. No particular reason, just at some point in time, someone with either money enough to have influence or simply being in a position of power, managed to make that the law. There may or may not be any actual justification for that ban.
But the fundamental basic of game & fish management here in the USA is that we primarily manage by bag limits, not method of take. For example, we're allowed one greater amberjack per day per person. Spear it, either free dive or scuba, or catch it hook & line, doesn't matter. 1 fish.
To me, how the fish is taken is irrelevant to management. You have x number of dead fish at the end of the day. if spearing on an RB was permitted, you'd still only have 1 AJ per diver per day taken at most, so the RB is irrelevant.
And AJ happen to be one of those really, really stupid fish. They''re in the running to be the stupidest fish out there. I frequently use the muzzle of my gun to push them out of the ay so I can see what's behind them.