The comment "level playing field for Main Street retail businesses" is just plain bad logic. The shipping charges that accompany Internet purchases are generally higher than the sales taxes at the brick-n-mortar stores. When a customer looks at total cost of purchasing over the Internet they include these charges just as they include the sales taxes when they purchase at a brick store. The big difference to the customer is that they have to wait several days for the Internet purchase where they get the retail purchase immediately. This is a huge advantage for the brick stores. The Internet stores have to offer incentives like better prices or larger selections to compensate for the wait.
When a remote state can levy taxes on a business with no physical presence in that state, it is considered Taxation without Representation. This goes against the fundamental principles of the Constitution.
Finally, the benefit that brick stores will receive from taxing of sales over the internet will be that the vast majority on internet companies will simply not be able to keep up with between 42 and 7,500 sales tax returns every quarter. In other words, except for the very largest Internet companies (Amazon, Barnes & Noble, Wal-Mart, Kmart, etc.) most other Internet stores will find they can not comply with the tax laws and close their web sites. This is the ultimate goal of the brick stores. Kill the competition on the Internet and raise prices. Everyone who purchases over the Internet will lose in the end.