I never mentioned the impact the taxes have on the poor, it's not really a huge concern for me. If the government wants to help the poor they can do so through extended, strong, social security nets, good education policy, and a strong progressive tax system. If the poor are doing something that is harmful to themselves then making them stop through tweaking the system properly will not hurt them in the long run, it will help them. Externalities are harms done to others by an actor. When a person drinks sugary drinks they are deciding to perform some action to themselves, it is not the case of the sugary drink companies producing things that harm others who have no control over the situation. People can, even if addicted to a substance, choose to stop using sugary drinks. You can't chose to or not to be effected by carbon emissions, you can choose to drink or not drink sugary drinks. The government should focus on ensuring people have that choice through information campaigns (informative ones, not propaganda ones). lung cancer through second hand smoke is a negative externality of cigarettes. Lung cancer in smokers is not. In this way the statement would be that smokers, who choose to smoke near other people should be responsible for the damages they do to them. In fact, they are, through higher insurance payments and high cigarette taxes. We can solve obesity without resulting to excessive taxes, but through setting up the system to function properly in the first place.I am unconvinced that the health consequences of consuming so many high fructose drinks are not an externality.
The way I look at it, lung cancer in smokers and obesity in the general population are both negative externalities because of the increased burden on our healthcare system. For people that do not have insurance or are on medicare (which is a significant portion of people), taxpayers and hospitals cover the cost of their poor decisions. There's the hidden cost right there. That's all a negative externality is: a hidden cost not reflected in the price of some good.
This is why I said that insurance companies should be able to charge more for things like smoking (they can), and without insurance in the US you have to pay for your treatment anyways. It is currently illegal in the US to not have insurance, so not being able to pay high costs shouldn't be a significant issue. As well, It is well within the governments right to charge for medicaid if they wanted to punish smokers for smoking, or people for living unhealthy lifestyles. A tax is not needed.
I understand your point, but it's not true that those without insurance in the US have to pay for their treatment. They owe money to the hospital that treated them, but they often don't pay it. Hospitals are not allowed to refuse service for emergency care. Additionally, while it is illegal in the US to not have insurance, the penalty is a small tax penalty, and the law doesn't stop a lot of people from still not owning insurance of some kind. I do think insurance companies should be able to charge more for things than smoking, but I think, while maybe not needed, a tax would help the problem even more.