But two brains could be conflicting, who you are as a person comes from your unique anatomic and chemical makeup of your brain developed throughout your life. Because of that, having two brains will make them conflict with each other, so you'd have major moodswings and extreme split personality, it wouldn't even be considered a disorder since quite literally there are two personalities inside you. And let's not even get started about the fact that two brains would conflict with your body such as control of the heart, lungs, etc.