depends on how much you spear and what your spear. If you are going for lion fish, for example, then it shouldn't be an issue if you are SCUBA diving vs Freediving - do people feel it is unfair to use a rifle vs a bow + camo + scentless cloths + plus sit in a blind and wait for the animal to come to them? I think that as long as the hunter is being responsible and not overkilling/breaking the law on how much fish to take/what size/what can and cannot be speared, it should not matter what method they use - just my opinion.
I don't spear fish (yet).