I think they weren't asking for an idea that would actually make the world a better place but rather one that somebody on some level believes would make the world a better place. Hence it still being a stupid idea.
If it were somehow magically possible to force people to use turn signals but only when they turn at intersections or change lanes, I think it would, in fact, make the world a better place. Because it would mean less car crashes.
But it's not possible, which is why it's a dumb idea.
It's not. The point of a turning signal is to give a warning to fellow drivers in advance. Turning it on right when you're turning is way too late. Just learn to drive properly for fucks sake!