It’s a terrible idea for a lot of reasons, but this bit from the link pretty much sums up why individual states forcing out-of-state e-tailers to cough up taxes just is not feasible:
Mary Osako, a spokeswoman for Amazon.com Inc., the largest online retailer by revenue, said state-by-state laws are creating a “very complex sales tax regime,” and that the company would only support a “simplified system, fairly applied to all business models.” Amazon is in favor a national streamlined sale-tax effort that would mandate sales tax collection by out-of-state retailers in 23 states that have voluntarily signed on to the program. “We aren’t opposed to collecting sales tax within a constitutionally permissible system applied even-handedly,” Ms. Osako said.
A 1992 Supreme Court ruling prohibits states from forcing retailers without a physical presence in the state to collect sales tax on their behalf. Many states technically require local residents to pay so-called use tax on such purchases, but most taxpayers ignore those rules.