Ask anyone who is obese if it's in their best interest and they're unlikely to say yes.  Same for credit card debt and gambling addictions.  These people know what is in their best long term interest but choose to do something else in the short term.  That's different from being "awful at figuring out what is in their own best interest".  People may be awful at choosing long term interests over short term interests but saying people don't know what their best interests are at all sounds condescending to me.