1) I had read several times that spearfishing is the most responsible way etc. Now, where is the hard evidence of that?
Well it is sort of common sense, what is worse for the fishery? Just observe and draw your own conclusions. A few guys going out and shooting 5-10 fish, or massive netting operations non-selectively pulling thousands of fish out of the ocean, and leaving nets and other trash in their wake? One guy underwater taking the specific fish he wants? Or hook and line boats with 40 people on them littering the reef the monofilament, lead, adding more trash to the ocean with lost plastic lures, and leaving hooks in fish they don't want? I don't know of anyone who has done a particular peer-reviewed study of it, but I think the reason why is because the benefits are obvious when you compare the methods.
I linked a study showing strong evidence of that.
I would disagree here. You linked a study that showed that fish population numbers in areas that tend to be hunted are different than those in a region where they are not. Again that is kind of common sense. If you define damage as any fish being taken from the water (which will reduce the population in that specific area until more recruitment occurs), then any fishing is "damage". The question is does spearfishing cause long term damage to the fishery, and is it reducing the populations to unmaintainable levels... Here I think the answer is no.
I see several flaws in this study as well... As mentioned before this study doesn't control for various factors... you can't take one area where there are virtually no rules about catch size, limits, seasons on specific species, and they are allowed to hunt practically however they want, and then compare it to a region where scuba is not used, but there are fisheries management policies, and say "hey look, this area is better, and its only because they don't spear on scuba". When you do this you are discounting all the other factors that actually produce the outcome.
2) from what I have seen so far I agree there is no apparent reason to discriminate scuba in particular. It looks even worse if the ban applies to any scuba regardless of spearing. What's the point exactly, locking people out entirely?
Agreed, which is part of the point, they are trying to pinpoint scuba spearing as a major cause of fishery damage, when it indeed is overshadowed by the larger number of people either 1) consuming mass harvested fish, or 2) the much larger numbers of sport hook/line fishermen as compared to spear fishermen.
Also for the record, the argument for banning scuba is a similar one. Don't allow people to scuba there because it causes damage to the reef. Many novice scuba divers step on coral, grab stuff, kick sand on top of hard corals that can damage them, etc. Just look at some of the dive sites that are frequented by commercial diving ops, and then go to a reef close by that gets little visitors and compare.
I am not saying I agree with their conclusion that maybe diving should be eliminated as well, I am just presenting what their argument is probably based on, and it shares parallels with their plan for spearing.. instead of better management and education, lets ban it.