Mostly what Atrios said. But beyond that, a political movement that’s interested in providing new public services requires revenue to pay for those services. To get the revenue, there have to be increases in the overall level of taxation. Those increase should take a progressive form — the rich should pay more.
But it’s absolutely crippling to any effort to outline policy with any level of ambition to concede the idea that any tax that places any burden whatsoever on the non-rich is therefore unacceptable. It’s fairly easy to design revenue measures that fall mostly on the rich, but extraordinarily difficult to design measures that exclusively snag people who fit a conventional definition of rich. It’s true that a married couple composed of an NYPD detective who pulls lots of overtime and a NYC public high school teacher with a lot of seniority can have a joint income of over $200,000 a year but a tax hike on the $200,000k+ crowd is still, all things considered, an extremely progressive measure.