There are many actors that want to convince you something bad, is good. Historically, cigarettes, sugar, even cocaine were advertised as healthy, or as better substitutes to things. Hell, even grain is still pushed by industry and government, when low-carb has a lot of evidence backing it.
Guess what happened when we decided "telling people sugar is great for kids" was bad? The government now regulates the information people are provided regarding nutritional content in food.
Speech isn't so easy, which is why the analogy still doesn't work.
I do agree, I wish we could live in such a world, but we indeed do not. That's why economics professionals receive nobel prices for their investigations into nudge economics and imperfect trade systems
Cows are not perfect spheres, and people are not perfect rational agents and that won't change for the foreseeable future so policy makers need to handle things with their avaliable policy tools, not the tools they wish they had
I prefer to live in a world where both are available and the preferred solution is education about the effects of junk food.