Except they're totally not, and saying that is dangerous.
Go look at crash tests of "child car seats" that are nothing more than a box ticking exercise which uses the adult seat, versus a properly engineering seat and you'll see what you are completely wrong.
That Freakonomics article is from 2007 and was only pointing out that manufacturers don't test all scenarios - not anything resembling your claim that they're just "safety theater". CDC strongly disagrees based on actual accident data (click risk reduction at the following link):
Go look at crash tests of "child car seats" that are nothing more than a box ticking exercise which uses the adult seat, versus a properly engineering seat and you'll see what you are completely wrong.