How do I stop myself from saying hurtful things?
Resist the urge to say things in the moment. In the heat of the moment, you may think (and end up saying) angry or even hurtful things, and if you allow yourself to vocalize those thoughts, there's no way to take them back. Take a breather any time you feel like saying something hurtful. Ask your spouse to do the same.
Is it bad not to argue in a relationship?
Fighting is never healthy in a RELATionship. The whole purpose of a relationship is to relate to the person you're in the ship with. The reason that a lot of couples fight is because they get together mostly off of their physical attraction to each other and less off their actual compatibility.