Pets are family, so people have a knee-jerk reaction to anyone badmouthing their pets even if the other person has a point.
My sister has a rescue pit. He's the sweetest dog ever - he was afraid of men for a while due to his previous owner, but gradually warmed up and now runs up to everyone he sees for cuddles.
However, when they took him to visit someone in a nursing home he ran off and bit one of the staff unprovoked. It turns out how a dog behaves around family versus around strangers are two completely different things, and dog owners rarely see the latter so judge their pet's personality based on the former.
A dog can be an absolute angel around people introduced to them by someone they love and trust, but if their little doggy brain registers someone as a threat (or even just an intruder in their space) things can go very wrong, very quickly.
This is a feature that has been sadly uncommon since Dungeon Keeper introduced it way back in 1997.