Ultimatums are NOT against DB. There is a part in DR I believe called "after the last resort", which talks about ultimatums.
It just says that an ultimatum is just that--the last resort beyond all last resorts. You have to know when you do it that it could go either way and be prepared for that. If you give an ultimatum and then you gave or backpedal, you have lost all credibility with your spouse...
