Forget the actual topic under discussion -- whether or not Amazon should be forced to collect sales tax -- and look at the mental processes at work inside the mind of a tax lawyer. It's no wonder our tax laws are so Byzantine.
You have to look to the nature of the link or connection between the state and the transaction. That link shouldn't be limited to physical presence any more than it should be expanded to include merely having an online presence.
One factor to consider is the solicitation of orders. Targeted advertising inside a state, including TV, radio and print ads, may not by itself be determinative but is a piece of a bigger picture. Also important are local agents and affiliates. Despite arguments from Amazon, I think states like New York and California are getting it right when considering locations of affiliates.
How and where orders are processed also matters. The location of warehouses, telephone operators and return centers should be part of the equation.
Finally, I think that you have to look to whether the retailer gets anything in return. What kinds of services and protections are being offered to the retailer inside the state? Does the retailer benefit from access to state courts, police protection and transportation systems?
There's not an easy answer to many of these questions. But then, when it comes to tax, you wouldn't expect anything different.
Do I "expect anything different" from a tax lawyer? No. But maybe that's a flaw with tax lawyers and not a problem inherent with collecting revenue for operating the government.