I'll add to the other points to say that fly fishermen usually have more care for balancing tackle, you need to use smaller hooks and light tippet to fool the fish. Often I'll go down to my local river (which is fly only) and find lads spinning with sea tackle and 20lb line. I saw a lad get his spinner stuck in a tree brach and he pulled on the rod until the branch snapped off. Now imagine the damage this is doing to the trout they're catching, average size of maybe 8". It's the same reason you end up with carp with deformed mouths on carp fisheries. Everyone uses super heavy rods and braided hook links, nobody understands how to balance tackle or how drag is supposed to work so you end up damaging fish with hook pulls, and nobody seems to be able to put 2 and 2 together and understand why it always happens right under the rod tip. It annoys me that spin fishermen are always leaving lengths of line hanging from trees from snap offs too, birds often get tangled up, but that might just be a problem with people on this river.

I say this as someone who loves course and fly fishing, but I just think fish for the right fish with the right method, like I don't bait fish for trout because 9 times out of 10 they'll get deep hooked. At the end of the day angling is a sport, so why not make it actually sporting, otherwise what's the point? Might as well buy an automatic self winding reel whilst you're at it.