Do not assume accidents are predictable nor likely just frontal, nor just a single impact. The issue is once a seat moves ( likely does not rebound) in any direction that loosens the belts, the belts serve little use in any additional impacts from any direction. I think comparing the intended purpose of a seat belt in a thin skinned alum tube that can reach mid 3 digit speeds impacts with the ground to a steel purpose designed forimpact cage at barely 3 digit speeds with an occupant wearing a rated helmet is not overly useful. twocents

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.