If Supply-Side Economics Was True, Would Liberals Embrace It?

Kevin Drum asks the long-simmering question of why it is believers in supply-side economics think liberals refuse to embrace this super-easy means to generating revenue:

The only answer I can come up with is that conservatives are now completely invested in their theory that we liberals loathe rich people so much that we don’t care. We all want to screw the wealthy so badly that we’re willing to forego the elections we’d win and the mountains of revenue we’d gain if we lowered their taxes. We hate them that much.

To play devil’s advocate here, is this really so implausible? It seems to me that I’ve read an awful lot about the evils of income inequality over the past 10 years. If cutting taxes on the rich increased inequality, but let the government raise revenue to finance much better bus service, is that something Kevin Drum would support? My impression, particularly over the past year, is that lots of my colleagues in the progressive blogosphere are in fact very worried about relative incomes and don’t believe that increased public services are a viable counterweight to a flatter income distribution. Right?

I think the right question to pose to the supply-siders is why they have such a hard time convincing public sector trade unionists to join their cause. If you work for the government, then support for more revenue should be a no brainer.