I think the issue for me is what behaviour people see as dominant. I've met so many people with reactive dogs whose behaviour stems from fear not dominance. To take a forcible approach with those kinds of dogs can lead to all sorts of issues.
We have a dog here that lunges, hackles up, growls and barks at other dogs. Does she do this because she is aggressive and trying to dominate the other dog? Nope. She does it because she is absolutely petrified of other dogs and thinks a good defence is a good offence. Everything has to be positive with her and anticipating and intervening when you can feel her cross that threshold.
Yet there are people out there who believe she is showing dominant behaviour and that I should discipline her for it.
Also just because a dog looks to a human like it is in charge, doesn't mean that this will always be the case or it is actually the 'alpha' of other dogs in the household. Dynamics can change over time especially as dogs get older and quite often if they are of the same gender.
I don't like Cesar Millan because he usually tends to provoke a negative reaction from the dog, flood it until it submits and then that's it. Real training is about reshaping a negative behaviour, not just repressing it through sheer force. There was one episode where he went into the yard with a white German Shepherd and the poor thing was absolutely petrified and he gave it no release of pressure even when all it was doing was trying to get away.
If you dumped a strange man into most people's backyards who then chased the dog around with some sort of bucket in his hand I bet most would react on the defensive.
This is my main issue when people start talking about being boss and quashing any show of 'dominant' or 'aggressive' behaviours. You'd think talking to some owners that anything their dog does to the contrary to their wishes is dominant when really it's not.