So you are talking about oranges while others discuss pears. If detriment is what you have defined, then every number you have posted is useless. We need mass, velocity, etc for the occupants. We need to know the elasticity of their collision. We need to know if the occupants are restrained. The 50 and 100 km/hr numbers tell us nothing useful for your definition of detriment. Worse, your posts are only subjective.
As first noted, what you are calling ‘detrimental’ cannot even be discussed due to too many hypotheticals. Due to missing numbers. Due to facts not found in the OP’s original question. Irrelevant even to what the myth busters demonstrated.
Other answers are addressing a completely different “detrimental”. Oranges and pears. Your detriment cannot be defined by anything in the OP’s original post - a 100 km/hr car or two 50 km/hr cars. We can only say the car and occupant as a unit are confronted by twice the energy when one car does 100 km/hr. Nothing more.
To say more means you must define “where” energy dissipates in the car and in its occupants - with numbers and vectors. I posted “where” in at the start. Your question in post #57 was repeatedly answered by “where”.
newme - it’s simple. Is detriment a relationship between the occupant and the dashboard? Or detriment defined by the energy that turned metal into scrap? Even the now moving car dissipates energy ‘detrimentally’ as tire rubber is ripped off by the pavement. “Where” does energy dissipate? robby says he is concerned with physics inside the passenger compartment. But then subjectively argues about energy that converts metal to scrap. Why is he concerned about energy dissipated outside when his ‘detriment’ is should be concerned with how hard the head hits a dashboard?
Why do politicians so easily manipulate the naive? The naive forget to define a problem before answering the question - as we have here. Or have brain pain rather than learn how to do the work. Always define a problem long before trying to answer it. Always. Otherwise scammers and politicians seek you out.
For most, ‘detrimental’ is the energy expended destructively into both vehicles. That includes any brake wear used to stop a once parked vehicle. When is that energy highest – most detrimental? When one vehicle at 100 km/hr strikes a parked vehicle.