All that is true, but in real world, knowing you will get ill can (and probably will) make a difference in how you can live your life.
Besides medical related issues, most insurance companies (in my country at least.. but if some tecnology like that pops out, surelly will start to pop out everywhere) require you state all medical conditions prior to the purchase of the insurance. And this insurance are mandatory for all kind of credit.
In the case of my country what they ask is for Known/Diagnosed medical conditions. So, knowing will give them legal basis to... basicaly abuse you. Making you some kind of type B, gattaca style, human being.