On your principles, you should never yield; you should be prepared to be defeated. Nobody likes to be defeated, but you should let everybody know in the most articulate and thoughtful and civil way you can (you don't go out and pick fights with people) that in certain matters that you define as matters of principle you will not budge, you cannot yield, you will not compromise. If you don't have the votes or the winning argument, then you stand to be defeated and rolled over, and you'll just have to come back another day.