It really isn't.

Ignoring that someone getting jerked around by The Gig Economy won't have time to nurture a kitten, people REALLY need to properly secure pets in a car. It is fun when they are wobbling around in the back seat when you are driving around.. until you need to stop suddenly or get rear ended or have a more severe accident.

Cats are much less willing to be restrained in a harness. But there are some carriers that are designed to be properly restrained and... it still won't be good for the kitty but it will at least minimize how far they go flying.