Say what will about Liberals vs Conservatives, Democrats vs Republics, that isn't the issue here. The issue is whether or not California, a state, has the right to collect sales tax from an entity that, legal speaking, isn't selling there. SCOTUS has pretty clearly said that it doesn't have this right.
Now, in an effort to raise revenues, California has tried to tax them anyway. Why? Because many of the roughly 25 thousand affiliates "forgot" to include their affiliate income. California would like to have this money and the online retailers are easier to come after than all of those affiliates. Frankly this isn't Amazon's problem, at least so far as California is concerned. California is trying to control interstate commerce. And as much as I don't like the over application of the commerce clause, this is EXACTLY why it's part of the constituation.