So, what do you think? Is it a bad thing to put a muzzle on a dog? Most people would say, "it depends". It depends on whether or not you think the dog is going to bite you. It's a little more complicated than that, though.
First, you have to recognize the subliminal anti-muzzle feeling you have and realize that it has no rational basis. While I always evaluate the pros and cons of using a muzzle, I also have this irrational anti-muzzle bias that comes from one source: Disney. There may be a lot of Americans who haven't seen "Lady and the Tramp", but there aren't many dog-owning Americans who haven't seen that movie at some point in their childhood. Don't get me wrong -- it's a great movie and a lot of fun. But think about this: all kinds of terrible things happen to Lady when she gets lost from home, but what is the very worst thing that happens in the whole movie, the biggest big deal? The muzzle. Sure, she almost gets gang-you-know-what, beaten up by bad dogs, run over, put in the pound, faces euthanasia, but that horrible muzzle that the horrible old lady puts on... Hey, I have been marked for life by that muzzle.
You think I'm talking psychologically marked, but I'm talking about my hands. I don't put the muzzle on soon enough, and I get bitten... lots of times in 28 years.
So, when is "soon enough" to put on the muzzle? The question is really "Why use a muzzle?" The simplistic answer is "to keep the dog from biting you", but that's not good enough. Why does he want to bite you? Maybe he's just frightened. Maybe he's a vicious man-eater. Maybe you're doing something that hurts him. Maybe he already got you! If you're bleeding, that should be a clue.
Oddly enough, most dogs will put up with a lot (including being stuck with needles) without much protest. After doing this for such a long time, I can usually tell when a dog is not going to tolerate the usual invasions of privacy. When I see impending disaster written on that dog's face, it's decision time, and here's how it stacks up.
1. What you're going to do doesn't hurt, and won't take more than a few seconds, but the dog is scared or aggressive. A muzzle is appropriate.
2. What you're going to do will hurt, but just a little, and just for a second, like drawing a blood sample, or trimming a broken toe-nail,or giving an injection. A muzzle is appropriate.
3. What you are going to do is really painful or will take a long time. A muzzle is only appropriate for a long enough time to give the patient a sedative and pain-killer.
4. You want the dog to be quiet. Muzzle is not appropriate.
5. You don't want the dog to chew on things. Muzzle is not appropriate.
There are muzzles that don't restrict the dog's breathing or drinking. They have big open baskets on the end. If you had to leave one on for a while, that would be what you wanted. They are easier to pull off than the ones that fit tightly around the dog's nose. That tight kind is better for most biters, but NOT appropriate to leave on for any length of time, as they do restrict the dog's breathing.
I don't put a muzzle on very often, not often enough, in fact. The scars on my hands look like an Arkansas road-map. Sometimes you need one, though, even if "Lady" was horribly scarred by her experience. Her psyche is in better shape than my hands.