While I agree that there are some underlying social and economic issues that contribute to obesity, that doesn't mean technology can't help. There are plenty of ways even simple apps can be used to improve people's awareness of what they're eating, help them make better choices, and provide incentives to eat better and get more exercise.
To address a couple of the things you mentioned:
Better education: It's true -- when it comes to health and nutrition, there's a lot of misinformation out there and a general lack of knowledge of even the basics. Most people are not great at determining how many calories are in a meal, whether something is good for them, or even just remembering what they've eaten on a given day. There's a huge opportunity for technology to help people figure this stuff out and learn to make better choices (full disclosure: I work on an app in this space [1]).
Taxing unhealthy food: While we can't levy taxes, there are ways to provide similar incentives, for example by automatically giving people cash rebates when they purchase healthy food [2].
Can the tech industry solve obesity on its own? Maybe not. But I'd argue that trying to address what we can is a better option than throwing up our hands and saying it's a social problem.
[1] https://getbitesnap.com
[2] http://www.nutrisavings.com
