I think it's regressive because people with less income spend a larger proportion of their income on gas.

I disagree with him; for the record. Just trying to see his viewpoint. Personally—I think this tax is a great idea. I think the government has two jobs: (1) to build and maintain effective infrastructure for the common good (roads, firefighters, etc.), and (2) to apply pressure to rectify forces where the tragedy of the commons would otherwise apply (global warming, etc.). This is an example of the latter.

Rich people may buy more gas, but gas eats up a considerably larger portion of the poor's wallets.