Is aggressive behavior always negative?

No - guardians and livestock protection are supposed to have aggression as a large part of their makup. Aggressive behavior towards family members is negative.[/color] 

Do you think it belongs to guard dogs?

It is not a guard dog without it - see watchdog

Can a guard dog be good without aggressive behavior?

It is not a good guard dog without it - see watchdog. 

Is growling and barking for all people aggressive behavior?

Barking for all people - tha's a good watchdog. For all strangers entering property growling and barking it is good behavior... dog should relax when strangers are introduced properly.

Can there be dominance without aggression?

No - it is like smoke without fire... it is the communicated threat of aggression which provide the non contact dominance.

Can a dog be a good protection dog without aggression?

Yes what makes the difference between guarding/protective behavior and aggressive behavior?