People choose to categorize a dog, and consider them an "aggressive breed". The problem is not the dog itself. It is the owner. The number one group of dog breeds that are considered aggressive, would be the bully breeds. Pit-bulls, Dobermans, Bullmastiffs, Rotweillers, exc. These breeds are the ones that have the most write ups on them, most complaints, and are categorized to be aggressive. If you look further into each breed though, you will see they're not just aggressive, they can also be great pets. It's all in the hands of the owner.
People, who do not train their dogs, socialize their dogs, and correct bad behavior, of course run the risk of having an "aggressive dog". A Poodle can be aggressive, if not trained correctly. The biggest mistake people make, is not getting their dogs into training right away! It's not only the large dogs, or bully breeds, that need to be in training. It is all breeds. Dogs are animals, and they have animal instincts. They were at one time in the wild, and had to fight for their own, and had behaviors that we as humans having them in our homes would consider unacceptable. Your dog needs to learn all his commands. Sit, stay, lie down, come exc. These are all key basics to the beginning stages of training. You need to be known as the "Pack Leader", in your dog’s eyes. Dogs constantly fight for the "pack leader" status. If you do not dominate your dog and make it clear this is your status, he will take over and control you. This is not good, and gives the dog power, therefore leading to aggression.
Another key responsibility you have as an owner is to socialize your dog. Un-socialized dogs become very territorial. This will lead to aggression. The last thing you want is a friend to come into your home, possibly startle your dog, and end up with a law suite or trip to the hospital on your hands. Socialization gives the dog a sense of friendliness towards other people. He learns when a person is threatening, or "just a friend". When you have a breed that others consider aggressive you want to be sure to do all of these things. Breeds such as the Pit-bull, Rotweiler, Doberman, exc. need a lot of socialization. They are known to be very territorial, and this behavior you want to correct, so your dog can determine when there's actually danger, or if it's okay to greet a non house hold member.
One of the breeds that have been most discriminated against, as aggressive is the pit-bull. Unfortunately in a lot of cases, these dogs have gotten into the wrong hands. People have turned these dogs into "fighting dogs". This is not acceptable, and because of the irresponsibility of their owners, some states such as California are now trying to outlaw these dogs. It is not their fault that they must die because of human stupidity. There are still good pit-bulls out there. Now they are so far gone in the stereotypical world though, only those that care for them properly will know what a great dog they can be. It's unfortunate that the irresponsible pet owners have turned them into such a feared dog.
To correct the world from categorizing dogs as "aggressive breeds", we need to take care in training our dogs. It is humans that have made dogs aggressive. We have not corrected the behaviors that are no longer acceptable. In some cases like with the irresponsible pit-bull owners, they have encouraged, and made their behaviors worse. So next time you see a snarling "aggressive breed", shake your finger at the owner. He has not taken responsibility as a dog owner, and because of that some one may get hurt, but those people should have a large fine to pay!