Yes, speeding might be a bad analogy, but that doesn't mean the argument is wrong. There are hundreds of good analogies that you can come up with, that people don't seem to complain about. For example, in NYC, restaurants are prevented from using trans-fats in their foods -- which prevents diners from choosing a tasty trans-fat-enhanced restaurant meal and deciding for themselves whether the health risks are worth it.
Somehow the supersize sugary drink thing seems to have angered a lot of people, drawing absurd analogies and slippery slope fears. As the article points out, the principle of the government protecting people from their own bad choices is already well-established, particularly when the damage of the bad choices is partially socialized, in the form of increased health care costs that affect everyone, via medicare, medicaid, or higher insurance premiums.
So, each case should be decided on its own merits, rather than hyperbole about the creeping nanny state. What the NYC law does is prevent companies from profiting from the well-documented tendency of people to overconsume when sugary foods are presented in large portions.
Other examples off the top of my head:
Credit card regulations. You are only allowed to enter into credit card agreements that the government approves of. If you want a credit card that has a lower APR but bunch of hidden fees, because you think you are smart enough to avoid the hidden fees, you can't.
Lead paint. If you want to paint your house with lead, because you think the benefits of lead paint outweigh the harms to your family, you aren't allowed to. The government says no.
Medical licensing. If I want to save money by getting surgery from a person who hasn't been to medical school, I'm not allowed to. I can only get my surgery from people who the government says are qualified.
Product safety. Pretty much any product safety law comes under the "nanny state" umbrella.
Motorcycle helmets. Any law requiring people to wear motorcycle helmets obviously infringes on people's liberty, for the sake of their safety. OK, some people do complain about these, but nothing like the sugary drink thing.
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