Dogs are animals and as such they have animal insticts. If you keep any animal you live with the risk that although you may feel you know the animal well and trust it, it still is an animal and cannot be 100% predictable. Some animals present small risks, such as small pets like hamsters and rabbits, and some larger risks. If you keep a dogs such as staffies, Rottweilers, mastiffs etc, then the risk you take is much greater. If the animal loses its temper and bites then it’s likely to be very severe.
Also you have a responsibility to protect others from those risks or accept liabilty if anything did happen.
Personally I believe it is selfish and irresponsible to keep dogs of this nature if you have children or expose your dog to others. Would you keep a lion as a pet, if you had raised it from birth, and expect it not to attack someone, or yourself? You’d be an idiot to think it couldnt or wouldnt.