Proper etiquette is to get permission since the landowner owns to the center of the road. It is common sense elsewhere.
How about someone from the Game Fish and Parks Department address the following:
1. Game Fish and Parks Department does not allow retrieval of big game without landowner permission. Why do they allow retrieval of a pheasant?
2. Game Fish and Parks Department protects their land by not allowing toxic shot. The landowner does not have the right to protect their own?
3. If the landowners grass in the ditch is so important then how about the Game Fish and Parks Department reimburse the landowner at the going rate for walk on areas.
Well, if you are going to hunt public rights-of-way only with the permission of landowners, you may as well stay home. I do ask if I size up a spot that is legal, but in close proximity to a house, livestock, etc, They usually say "I would rather you didn't, but thanks for asking". That's good enough for me.
In response to your three points:
1. Hunting of big game from a public right-of-way is illegal, even if you are the one paying taxes to the centerline. Therefore, by design, retrieval of a big game animal from private land is illegal as you broke the law simply by shooting. I don't think I need to address the ballistic differences of a shotgun versus a high-powered rifle. Remember, if flight originates from the private side of the fence, you are breaking the law by shooting, unless the bird's flight path takes it over the right-of-way.
2. We all know that the days of lead shot are numbered, however, I have never heard of it causing any poisoning of livestock, etc, simply from road hunters shooting over private land. If this were a major concern, don't you think landowners would dictate non-toxic shot for their paid clients? ( I am sure some do, but far and away, most don't.)
3. The landowner's grass is his/her decision to manage,most of it is cut for hay, therefore they are being paid for it. If they have the smarts to leave some for wildlife habitat, it only benefits them, overall by reducing erosion, etc. Also, landowners are allowed to hay their walk in land. It does not become off-limits to the owner simply because they sign a contract with GFP. Many walk ins are hayed or grazed long before hunting season. This reduces the value to sportsmen, but on balance, the walk in program kicks butt.