Not being a spearfisher, I don't really have a dog in the fight.
I can say from a personal safety standpoint, I would feel better going out on a rig dive if I knew my boat mates would be freediving to spearfish rather than prowling around the whole time on scuba. I guess I would have an easier time keeping track of where they were and not feel like I was needing to look over my shoulder the whole dive.
From a very distant perspective, it does seem more sporting to spearfish while freediving rather than on scuba.