I just watched a sweet little video featuring frolicking pit bulls that made the statement
"Responsible ownership can prevent any aggressive tendencies"

Well, no, actually it cannot........

A lower threshold ("tendency") for aggressive behavior is NOT all based on how a dog is treated or trained. It's also part of an animal's DNA.

Predators need both offensive (hunting/killing/taking) and defensive (reacting to a threat or challenge) aggression. Aggression is a normal and natural survival trait that wild and domestic canines use for defending territory, guarding resources, and catching prey.

You can (and should!) suppress aggressive behaviors with training & conditioning. Just because aggression is a natural instinct doesn't mean it should be tolerated! You can manage the dog's environment so that it never has to interact with anything that might provoke it. You can use fences, barriers, leashes, bite guards, and muzzles... but it's very hard to entirely smother a trait that a dog is born with.

Experiments have shown a variety of genetic, epigenetic, and environmental (including while still in the womb!) factors can influence reactivity thresholds. Breeds are not uniformly docile or aggressive. Some individuals are very quick to react. Others take quite a bit to provoke to anything *like* aggression. It's far more important to be able to read a dog's stress and arousal signals than to recognize what breed it is.

Owners of reactive dogs watch vigilantly for triggers and limit their activities to safe pursuits. It may mean no doggie daycare or visiting the relatives or sniffing other dogs while on-leash. But often these are fun and highly-sensitive dogs who are great to live with. Owning an aggressive dog does not necessarily indicate that you are an irresponsible owner or did something wrong-- or that it's a "bad" dog. It's just a trait you have to work on and manage.

After all, there are worse things than an aggressive dog.

You could have gotten an aggressive cat.