Here, in a recent speech, is what Marion Nestle offers in response to that argument.
I have trouble with this first amendment argument. I imagine back to our forefathers who wrote the first amendment sitting around a table saying, “how are we going to guarantee freedom of speech for people who have diverse religious beliefs?” They were NOT sitting around that table saying, “how can we defend the right of makers of junky cereals to market their products to kids?” I think we have a real problem with this. Some lawyers should take a look at the first amendment and start using it for what it was for.
*Slight edit 9/15: made more clear that I am summarizing an argument, not stating my view.