It's far from one of his best articles and his comments on it's use for flying game are nonsense both on the face of it and logically. There are several grounds for his dismissal of the cartridge's suitability, among which is his statement that the stock fit is wrong, which is a sweeping statement that obviously doesn't stand up to examination.
"I think it is morally reprehensible to discharge missiles with lethal force at a sentient being without being confident that you will inflict as near an instantaneous death as possible. If you want sporting targets, take your .410 for a round of clays and don’t put living creatures at risk of suffering when you don’t connect properly."
This argument disqualifies the use of anything but the heaviest firearm possible on all targets. The same objection applies with equal force to the use of 28 bore, 20 bore, etc. etc. It also disqualifies his own use of the thing on stationary quarry. Whether a creature is moving or not makes no difference to the ballistics of the cartridge.
"In similar vein, somebody at
The Game Fair this year claimed the .410 was the ultimate sporting shotgun because… it either delivered a “kill” or a “clean miss”. How anyone could say such a thing is beyond me. There is no way of knowing whether the pheasant you have just failed to bring down with your .410 has missed ‘cleanly’, and therefore it is not a risk any of us should be willing to take. "
The same argument applies to all firearms, and indeed all methods of killing any animal. Things can and will go wrong with any system.
The fact is that the pellets from a .410 have the same energy as those from any other gun. In the article, he states that nothing worthwhile is known about the exterior ballistics of the .410, and then dismisses it because of his assumption based on what he himself described as ignorance.