Perhaps you could catch gamefish in a casting net. But, since they are immediately brought to the boat or shore, gamefish would be easy to release. Since such nets are designed to catch small baitfish it's not like most fish are going to get caught by the gills or some other manner which would increase mortality.
Pretty sure changing the law wouldn't affect me much as I fish mostly with minnows in the winter and either leeches or worms in the summer. That and I would have to get way better at throwing the net than the last time I tried. Takes a long time to catch enough bait when the circle I was throwing was yielding about 1 or 2 baits/throw.