Look, if we want a competitive marketplace, it makes sense that everyone operates under the same tax constraints. This isn't a pro-tax, anti-tax, pro or anti commerce clause thing. It's just basic economics, the best services will float to the top that way.
No, it isn't fair to the retailer that ships to 50 states, since they unlike the local only retailer now have to file and keep up with tax laws for 50 states, not even considering all of the counties and stuff like that.
Everyone /is/ operating under the same tax constraints. The difference is, your local retailers aren't selling their products out of state like Amazon.