This is extremely false.

Car seats restrain the infant in a crash, greatly reducing the chance the infant/child themselves becomes a projectile. By your logic, seatbelts should not be mandatory on planes either. Who cares if your head hits the ceiling because you weren’t restrained?

A quick review of reports after various airplane crashes would support a very statistically significant increase in the chance of survival given the wearing of a seatbelt versus not wearing a seat belt.