Comment by TeMPOraL

To add to upsides:

4. Occasional anecdote about someone who knows someone who was in an accident while wearing seat belts, and the seat belts proceeded to slice their head off or cut the body in half or something else like that.

I assume an event like this happened more than zero times in the history of the world, but AFAIK it's too low-probability to worry about (with possible exception of kids under a certain age/height, that shouldn't be strapped in with regular belts in a standard adult configuration).