This is true in theory, but I don't exactly agree. Sometimes your silence can be "misquoted" as agreeing with what someone has said. There are times you need to make your position perfectly clear, so that your silence in not interpreted as agreement.
We all make mistakes. Even big betrayals can be forgiven. But if you wont stop what is causing another pain or even apolgise...well it shows you have no respect for that person. There is no choice for you but accept who he chooses to be or remove your self. Your boundries are not a value to them!