If you could wave a magic wand, what would you fix?

I would make everyone take an IQ test, and those who have an IQ of less than a certain amount will be sterilized.

Additionally, those who are not sterilized, will get sterilized after birthing their third child as just part of popping out the kid. They let the epidural wear off and sterilize the couple. Prevents overpopulation and people having kids so they can leach off the welfare system and reduces abuse and neglect cases because people who aren't smart enough to raise kids, won't have any.

Better yet, give ALL 18-year-old males reversible vasectomies. In order to have the vasectomy reversed, he must be at least 25 years, pass a test, and PAY to have it reversed. If he can't afford the reversal, he can't afford kids. The money he pays to have it reversed can be reimbursed upon successfully raising a child to 18.

The single largest problem facing us to day is us. We humans create all the problems that affects everything, hence we suffer as a consequence. Hence, all the problems will never be fully solved, as others will just be created. It is simply human nature.

I think that there are too many BIG problems to be able to pick just one. AIDS/HIV, Cancer, Racism, Debt/Poverty, just to name a few.