Because that's what it is. It's about using less energy. It's about using cleaner energy. It's about moving away from polluting industries and toward industries that provide us with the services we need and yet don't disturb the climate.
It will have to involve a carbon tax--a carbon price of some kind--whether it's a tax or a cap and trade system. It will have to. You don't get the reductions unless you have a regulation to reduce emissions or a price that compels polluters to reduce their emissions.
You can design a carbon tax or a cap and trade system in many different ways and, if you wanted to, make it completely revenue neutral from a government perspective. You reduce other taxes. You can also use some of that money to invest in the emission reductions we need elsewhere, like retrofitting buildings, or putting more money into transit, which we have a consensus needs to be done.