Why is it wrong for the government to encourage individual behavior through taxes and subsidies?

Human beings act based on their environment, we don't do things for no reason.

In this case, sugary drinks are popular for a reason, it is that reason we need to think about and combat, not attempt to stop people from reacting to the forces against them with taxes.

In this case we need to end the subsidies for farms and crops, to make it so that people pay true costs for their sugary drinks, and to allow the healthcare system to charge extra money for an unhealthy lifestyle. These are natural systems that adjust themselves over time and dynamically react to the forces on society.

A tax sticks around for ages, funnels money away from where it should be going, and sticks around long after it is needed.

Carbon taxes are a different category of things, in that we have an action that is an externality. The emission of carbon HAS to be cleaned up and offset, and companies today are NOT paying that price.

The point of a carbon tax would be specifically to offset the damage done by a harmful activity which is a fairly constant and ever-present issue in society. There will never be a time that a carbon tax is not a good thing, and it corrects a balance in the economy that cannot be fixed otherwise.

The government isn't paying for our healthcare, it needs to stay out of taxing us for the choices we make about our health. If it would like to charge those on medicare for drinking sugary drinks, than it is well within it's right to. If it is involved in investing in and pushing for the offset and cleanup of carbon emissions, than it is within it's right to charge for it.