I think the idea sprung up because it's easier to have a "problem" to fix than to admit that a relationship with your dog can be difficult and something that you have to work on. Humans seem to do this a lot and we like to have something that we see as fixable rather than something that we have to accept as "the way it is." Labeling a dog or a puppy as dominant or defiant takes any responsibility off of you for undesirable behavior and puts you into the role as "problem solver." It also takes the responsibility off the person if they have to re-home or give up said dog. It's not that they failed, it's the they had a "dominant/issue" puppy.
Mind you, this isn't everyone nor is it the only reason but it's the one that I see most often. Luckily, I was never flooded with this message but that's probably because I was just lucky as well I did my own research. I found the right books early on (Patricia McConnel and the like) and was able to find a great trainer to learn from with my first dog. She's still one of the most "dog savvy" people I know and I now see how lucky I am to have had her as a mentor before I got all the different dog theories
I totally agree with this statement. People use "dominance" as an excuse for everything they can't explain properly. I hear this day in and day out in my business. I do my best to explain to people that their dog isn't "dominant" and you don't have to stare your dog down or alpha roll it to get results. They believe everything they see on TV, from behavior explainations to dog food ads. That's why I call them "sheeple". Even as a professional, you can't change minds.
I, personally, have never had a dog be "dominant" in a pack situation. I rule my house and my rules are strict. I don't use any kind of adverse method such as "alpha rolling" my dog to establish my rules. I use NILIF and if they bicker, they lose privaleges to bedding, toys, treats. This snaps them out of it quickly. Of all the dogs I foster, dog sit, adopt, (I have a huge turnover in my house) I have never had an all-out fight based on "dominance". I've had spats over the best toys or places to sleep when a new dog comes in. I've taken beds out of my house completely and re-introduced them via a "claiming ritual". The claiming ritual is that "I" sit on the bed and when I want the dogs to join me, I invite them over, just like you do with the human's couch and beds. This ends all the problems. Periodically, I will walk over, sit on a bed and ask my dogs to remove themselves. Just a reminder that I own that bed and I let you "dwell" there for as long as I'm ok with it.
I've collected the toys that were stashed around the house and taken them completely away. I will reintroduce a toy while I play with it and invite my dogs to come play,too. If a new dog comes in and tries to claim chews or anything, I manage it by taking all chews away and swap them among the dogs. I take them all away and give them each other's chews to munch on. After 15 minutes, I take them away and offer them to the next dog. It's musical chews. I have taken some hefty resource guarders into my house and have never had spats because of this method.
My dogs know there is no "second in charge". Humans rule the roost and all dogs are on the same level. No one tries to "take alpha position" from another dog because nothing belongs to them and there is no reason to do that as no one owns anything.
I'm sure I'm going to get flamed for what I just wrote, and I'm ok with that. This method works for me and I rarely have any issues, no matter what kind of temperment a dog has. I expect my dogs to comply, as a new dog has to learn these rules. That's why I go through the rituals when they come in, to show them what's expected. I've fostered all breeds of dogs and many different behavioral issues. Resource Guarding, people aggression, and dog aggression are the most common ones I take in. This works for me but it might not work for anyone else.
EDITED TO ADD: my dog share everything. They wait patiently to share affection, no pushing to get in on the action. They wait patiently for food, treats, they work together as a pack and accomplish a lot. They are laid back because they don't have to fight for anything they want. It's provided to them as they have earned their stuff. I spoil the crap out of my dogs, my husband says I spend more on them than I do on myself and that's true! They deserve it because they have worked hard for it. It's not easy for them with the turnover in my house, sometimes they meet the one dog who will challenge me. They enforce rules like counter surfing and jumping on people. They know they can't do it so other dogs can't do it either. They will correct but that doesn't mean they are "Alpha" because they correct. It's not that THEY don't want a dog counter surfing, they know I am the one who doesn't allow it.