Indeed, one disadvantage of the rebate method is that it forces everyone to "register" their families with the government. In other words, if you have a new child, and you want to make sure that child gets figured into the tax rebate (which, if you don't make much, you certainly would), then you have to notify the government. Not that they wouldn't already know.
Having said that there are two disadvantages with the food exemption. (Well, one real, and one false.) First, the real one: food isn't the only "necessity" we have. For most people, a car is a necessity, so is gasoline. The rebate takes all of that into account, a simple food exemption doesn't. Now I really don't mind exempting necessities from the sales tax---but if you start adding exemption after exemption it will get complicated, and of course there will always be an interest in adding a new exemption.
The other one, which I already said was false, is a class warfare issue. If you exempt food, then that means that the person buying premium food at higher prices (presumably, the richer person) will be in effect receiving a larger "rebate". If you exempt cars, then the more expensive cars will in effect give a larger "rebate." (OK, so you could exempt, say, just the first $10K of a car purchase, but again, there's the complexity.) Like I said, this is not a "real" disadvantage, it's a political one---it's an angle that class warfare nuts can exploit if they are so inclined.
"Indeed, one disadvantage of the rebate method is that it forces everyone to "register" their families with the government. In other words, if you have a new child, and you want to make sure that child gets figured into the tax rebate (which, if you don't make much, you certainly would), then you have to notify the government. Not that they wouldn't already know."
-- If you have a child, you register with the government ANYWAY when you get a social security #. This is a total non-issue.