If your purpose isn't worth you speaking up for, then you should reevaluate whether or not that's your purpose. 

Your purpose is fueled by passion and I've never met a passionate QUIET person. Granted there are people who are very passionate about their purpose, their skill, their calling and they're naturally quiet people UNTIL you do or say anything that threatens their purpose and the inner beast is unleashed. It' not malicious. It's passion.And passion is what fuels your purpose. PURPOSE is the engine and PASSION is the fuel. AND ANYTHING you're passionate about... you don't keep your mouth shut about. Speak up for your purpose.