The USA should offer every person who turns 18, the option to get $15k in return for the government paying for their sterilization or their tubes tied.

This would drastically reduce the number of people who shouldn't be producing. People who can think long term have drastically higher IQs and are much more productive members of society. So if someone is unsure of having kids at 18, they wouldn't take it. But if they just look at the money and think "I could buy a used Dodge Challenger with that and maybe get my pee pee wet!" then chances are you are better off not reproducing.