i have had the exact opposite experiences with cottonmouths. they are one of the most lenient venomous snakes. i have accidentally stepped on them many times and not been bit, and my son has as well. my guess is that your pets probably tried to kill them or messed with them in some way. they can definitely do some damage, I have seen people lose their entire calf muscle or parts of their hands from cottonmouth bites, but it is a rarity, and you shouldn't just go out and kill them for little or no reason.
Cottonmouths are also the most durable, resilient snake I have ever encountered. they will eat roadkill, even other dead cottons, they can survive harsh winters without hibernating, eat things that seem impossible to eat, and still behave rather gently.