dogs are social animals. that people adopt to have around children.

dogs raised in poor conditions get a kinda "ptsd" and can become violent at the flip of a switch. because the dogs have to try to fight for survival.

then theses dogs get aroundchildren and some tiem hurt the children.

but shelters put down any too violent dogs. and shelters are more likely to have volunteers to walk the dogs daily. so the dogs are generally more calm and relaxed. and less likely to snap and hurt people.

IIRC chickens have to have their beaks cut off in chicken mills because they go insane and start eating them selfves or their neighbors.

IIRC most bulls/cows /steers get de horned because they start attackeing eachother if caged in too small fo enclosures.

IIRC pigs have to be seperated and drehorned also because they become violent and agressive being caged

tl:dr; it is my opinnion that the difference is children. you would never ever let your child be in the pig pen. the pigs will literally eat your child alive. dogs raised in mills get that same aggression.