[giantg2]

"The idea is to protect lighter weight occupants who are wearing seatbelts;"

Not exactly. Lighter weight occupants are not supposed to be in the front seat wearing a seatbelt. The same places you're getting the warnings for not placing child seats in the front seat will also tell you not to put children in the front seat.

They try to plug it as a safety thing as a way to protect ignorant consumers from themselves.