"Don't design a behavior that the a user wouldn't want if they knew everything that we know." -- @nireyal This is similar to how I've though about this, but in practice, I have found it very hard to tell a "bad behavior" from a "behavior that is not for me." For example, there is food that is bad for you and food that is not to your taste, but without the science of nutrition it would be really hard to tell the difference. I would never eat a steak well done, but I don't think it's immoral to cook it that way for a friend if that's how they want it. I'm also on the hunt for a better moral principle and I'll let you know when I find something.