I think he's saying that individuals that sell online shouldn't be taxed by state legislators they didn't elect. Congress won't be setting the internet sales tax rates, nor administering the tax, nor conducting its audits -- the 50 individual states will be imposing their individual rules.
If a foreign state I've never stepped foot in can set laws I have to obey, force me to remit money to them, and audit my accounting under penalty of imprisonment, it doesn't really matter who's doing the paying. Today, only people within the state can be forced to obey and be audited by that state. This bill gives the power for a state to create and enforce arbitrary laws on non-citizens. It's at least a sufficiently different situation to debate.
Boy would I prefer a single federal sales tax with the fed doing the distribution to the individual states.
That's what happens when you do federalism only when it's convenient. Right now since "interstate commerce" is extended to cover any activity that may be imagined to be related to commerce (including growing plants in your own garned for your own benefit) it means federal government can force commercial entities to do anything. Including complying with foreign laws (including non-existant foreign laws: http://www.threefelonies.com/Youtoo/tabid/86/Default.aspx#La...).
Single federal sales tax with distribution would result in either grotesquely complicated calculation system or some states sponsoring other states for political reasons. And, of course, all local governments blaming federal governments for the lack of funds and their inability to do anything.