Actually, taking your dog in to be put to sleep sounds a hell of a lot more humane.
I don't necessarily agree with this. Though I would never be able to shoot my pet I can understand it since I am from a very small town and there are no vet services available there. One of my family members had a dog that was really suffering and instead of putting it through an hour and a half drive causing even more suffering and fear he did in fact end the dogs life with a gun. It was the hardest thing he's ever done. To me this doesn't make him a bad person.. the way I see it he was able to put aside his feelings and gave the dog what it needed. Peace. He threw up and cried for days.. wasn't able to sleep.. He loved that dog with all his heart.
I think that both a shot to the head, done right, and being put to sleep at the vet, are both humane. The difference in my opinion is that the vet route is obviously less gorey and easier to feel ok about. But from the position of the dog in question I don't think either is necessarily better than the other.
I'm certainly not defending people shooting pets for fun.. or for the wrong reasons at all.. but in some cases I do feel it is understandable. Difficult, but understandable.