Not nervous about boxers....but have had bad experiences my entire life with pits and pit mixes (live in nm where most of the time they are bought for the wrong reasons)...though I dont see my dog any diff or love her anyless.. Have seen how
small mistakes in raising them leads to all the neighbors chickens, sheep, and many times children being bit and or killed. So want to make sure I learn as much as possible from actual responsible owners of these breeds.

so excited to have her and learn!
Generally it is more like a serious of major abuse and neglect, not in any way small mistakes, that causes these dogs to be human aggressive. Chickens, well, that's just prey drive and nearly any dog will go for a chicken given a chance.
Dogs that are chained up are more likely to bite- they are often neglected, rarely socialized, encouraged to be "protective" which is basically a recipe for disaster.
Gross mismanagement is other factor-- there was a case of a mutt that killed an infant. The very very young infant was left alone with a large dog who it appeared may have just tried to treat her like a dog and "play." Entirely preventable and not even a case of human aggression.
The media also leads people to believe that "pits" have more bite incidents than they do... recently here the media reported so-called breaking news that a child had "almost had his hand bitten off by a pit bull." What a lot of people didn't get to see was the follow-up news story where they revised it to the correct facts that a child had been bitten (not severely) by a SHELTIE! Slightly different eh?
Edit to add:
Getting involved with a good group of responsible pit bull/bully breed owners is a GREAT way to learn a lot, see all the great things pitties can do, and get lots of positive interaction.
My rescue has dogs that are service dogs in training, dogs that go to schools to show kids how to treat dogs nicely and how to care for them, dogs that go to children's hospitals and places for abused kids to cheer them up etc.