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You don't have to force people to eat healthy food, but you can do stuff like tax food to represent the true costs of an unhealthy diet.
In any case this is wildly off topic.
(bolding mine)
Wildly off-topic yes, but I'd like to chime in.
Essentially what you are saying is that an unhealthy diet, and the consumption by an individual is an inefficient transaction, because there is an external cost to the, say, cheeseburger that isn't in the initial transaction cost at McDonald's.
If we assume that say for instance, the external cost associated with the cheeseburger that is not a part of the initial transaction ($1), is about 50 cents in the form of say, higher health insurance premiums, then the "true cost" of the cheeseburger is $1.50, right?
Your solution would be to impose a tax of 50 cent to every cheeseburger, and subsidize the public to balance the transaction, thus making it more efficient.
The problem with this type of "solution," is that it ignores the real problem. It's not external cost that is the problem, but the transaction cost. (Not between Mcdonald's and the customer, but between the customer and the insurance buyer)
Consider a simpler example to illustrate this point.
If a factory pollutes into a neighborhood down-wind, the intuitive response is that the factory is imposing a cost onto the neighborhood, and should thus be taxed for the exact cost the pollution causes, and the neighborhood should be subsidized that amount.
The inherent assumption is that the cost is only being imposed by the factory. This is where the tax/subsidy solution breaks down.
The factory is imposing a cost on the landowners, but the landowners are imposing a cost on the factory by living near the factory.
This can be seen very clearly if you consider the cost involved of the factory installing anti-pollution measures.
The point is that the actual cost is of transactional nature between the two parties, not a one way cost imposed by one onto the other.