OK, this is far-fetched and waaaaayyy too "1984" and Big Brother to actually be put into place, but read it anyway.
A friend of mine had this idea for a way to reduce unwanted pregnancies.
Sometime after birth, but before puberty, every person has installed a switch that controls the reproductive organs. Turn the switch on to enable the ability to reproduce. Turn it off to disable reproduction. Sexual function is not changed, only the ability to reproduce is disabled.
When a man and a woman are gettin' jiggy with it, one of them will always be able to prevent a pregnancy regardless of the other's intentions/responsibility/motives/forgetfulness.
Those that like to sleep around can safety-wire the switch into the "off" position to prevent mishaps.
Now that that problem is solved, I'm off to fix the bad drivers of the world. I'll start in Texas.