It's not stereotypes, it's called breed temperament. It's part of the overall breed standard defined by the club.
If you want a lab or golden, buy a lab or golden. Don't buy a mastiff breed. It's simple as that.
I do not think breeders should be breeding guardian breeds for friendly temperaments. Will you occasionaly have friendly dogs, of course, but it's not and shouldn't be the norm.
There is a whole gray area in between. Should people create monsters by leaving them chained in the back yard? No! But that is different from a well socialized, confident, aloof dog.
I expect my dog to be controlled, calm, and obedient to me. However I own a guardian breed for a reason (cane corso, presa, CAS, boerboel). I am aware of their temperament. It one reason why I love the breeds I do. While I don't expect (or let) him lunge, bark, and be frightening to everyone; I do expect a certain amount of wariness, alertness and aloofness.
I want my guardian breed dog to do what it was designed and created to do, guard. In public he should be watching his surroundings (it's a good thing to be alert), he should be uncomfortable and even give warning if something is not right ( people approaching at night, drunks or people being disorderly). He should not be happy having people fawn all over him. If I ask him to he will, but he doesn't like it and he gets HEAVILY REWARDED after.
I agree one should take every step to socialize and create a well adjusted dog. However I disagree that any guardian should approach life like a lab. Mastiffs should guard, labs should retrieve, collies should herd, terriers should hunt vermin, it makes the traits we love in our defined breeds. Just as a lab afraid of water would be no good, a mastiff with no protective instinct is pointless. It is the whole reason breeds were created in the first place, for a purpose.
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