On the one hand, I agree that it's unreasonable to require a small retailer to contend with the 10000 U.S. tax jurisdictions, much less the exposure to potential legal costs even if they do everything exactly right.
On the other hand, I don't see why they should be given the artificial competitive advantage of offering products without sales tax.
I'd like to think that a system could be devised that's fair to all parties while somehow closing the offshore loophole. In the end, it's the buyer who's responsible for paying the tax no matter where it comes from (Edit> or who collects it)...