How wrong does a parent have to be before you stop defending them?

How much thicker is blood when compared to water?

Suppose your parent picked a fight with a neighbor, accusing them of bringing a bad element into the neighborhood. But you didn’t agree with the accusation. When the neighbor verbally attacks your parent, do you automatically defend your parent, even though you think they are wrong?

This is probably a stupid example, but try to help me out. I’m trying to find out how far wrong a parent or sibling or child could go before you would stop defending them if they said something you didn’t agree with. When, if ever, do you stop being on their side?