Short answer is that no one has a right to shoot at an aircraft regardless of what it is doing. It should be charged as attempted murder rather than a slap on the wrist. All it would take is a couple pellet to the face to blind the pilot and no way could he land an aircraft when blinded. Many of the crop dusters have fabric covering the fuselage so that is little protection from even small shotgun pellets. This is a serious felony crime that should be punished to the full extent of the law.
In this case, I believe that the "full extent of the law" was some where around 20 years. The fact that the guy got a few months probation, has to "explain" via a news paper add, and has to develop some content for "young hunters" classes indicates that there were some extenuating circumstances.
If a crop duster were threatening my life, the life of my children, or my livestock with over spray, or was otherwise causing damage to my property, wouldn't I have a right to defend myself? Maybe I've been dealing with the same crap year after year, and all complaints and calls to law enforcement have been met with "quit wasting our time with you stupid airplane complaints." Maybe my law suit from three years ago was lost because the hundreds of thousands of acres of corn grown in my county brings in more revenue than my two dozen Rhode Island reds do, and my self-prepared case was no match for the $500/hour lawyers that the Crop Dusters Association provided for the pilot.
Granted, opening fire is a pretty drastic response, and you would HAVE to know there would be consequences. But there's more to the story than I've been able to glean from the assorted internet articles.
I was an Army pilot for a quarter-century. I can tell you that no one gives a crap about stampeded cattle, terrorized chickens, or innocent school children rattled out of their beds at two in the morning. Noise and encroachment complaints are so frequent, and often so frivolous that it all just gets lost in the background noise (no pun intended). It's not until someone takes a shot at you that you take their complaints seriously, and a three-mile no-fly-zone pops up around their property (and they probably go to jail). Heck - we were made to have more consideration for the villagers of Iraq and Afghanistan than here in the US.
Got to consider all the angles.