Seat belts have a primary use just like headlights, and neither is what the public thinks it is.
Seat belts are primarily to keep the driver in the seat, not to save your axx. If you lose control, then you slide out of the proper seated position and chances of saving it are virtually none.
Headlights are primarily for other drivers, and pedestrians, to see you, not for you to see. It does no good to have great visibility of surroundings with no headlights, when you pull out in front of someone who didn't see you. The headlights(all corner lights included), should be on in any non perfect visibility. It also doesn't hurt to have them on all of the time.
Try driving around a low speed autocross course with no seat belts. See how safe that is to do in a controlled environment.