13% of the 'half of all earners don't pay income taxes' are middle income earners with enough itemized deductions that they owe no income taxes. They still paid federal taxes, however.
You want to propose taxing them more, go ahead. Has nothing at all to do with widespread American support for exactly the kind of tax that Obama has proposed. It's the right thing to do, and you know it, even if you're arguing against it out of some partisan affiliation.