It’s amazing how people will lie to themselves about their loved ones even in face of evidence to the contrary.
Yes, you know and love them but no, you cannot completely vouch for everything they do. Don’t be stupid and put yourself on the line for someone else. We can never completely know what is in someone’s heart.
So stick up for them by all means – but don’t be naive and rule out all types of behaviour – because, well, you never know do you?