I disagree.

First, to stop the carrier itself from becoming a projectile, it has to be strapped down in some way. That can be quite difficult, depending on the configuration of the car and what style of seatbelts you have. Getting a 3 point seatbelt around a hard sided carrier in a way that prevents the carrier from coming off the seat is next to impossible in my car. Securing the carriers well enough to prevent them from moving around means using the tie-downs in the cargo space, a option nobody likes.

Second, the cat is not restrained within the carrier, so in the event of sudden braking or impact, the cat can be flung around with considerable force.

And perhaps most important to my cats, they can't see out the window from inside the carrier. All three are calm and happy on the road if they have a view out the window, but get quite distressed and vocal if they have to remain in their carriers for long rides.