When people say that dogs love us unconditionally, they are referring to how some dogs continue to seek human company, attention, and affection, even after being hit, beaten, neglected, and abused by us.
This does not mean that dogs love all people unconditionally, but that they have the capacity to forgive, forget, and love us again even after going through some tough times.
This does not mean that dogs do not feel pain or do not suffer from pain, nor does it mean that they are unaffected by abuse. It only means that they have the ability to bounce back if we give them the chance and help them to do so.