Taxing is the most important in the minds of statists. Without forcing people to pay, they would not be able to realize their dream of the all-powerful state.
I also sell on eBay and Amazon. They both automatically charge CA sales tax to California customers for me. If those sites could collect the various state taxes and automatically sent them to the states, I'd be fine with that. But if I had to file individual state tax forms, I'd just give up on selling online. (I'm nowhere near selling $100K out of state,so this would only matter if there was no ceiling.)
Maybe there should be one sales tax rate for online purchases so companies wouldn't have to fool with all the various state, county, city, special district tax rates. Say there's a universal 6-7% online tax. If I lived in a state where the tax rate was 4%, I'd still buy online for the convenience. I currently pay 9.5% sales tax when I shop locally. I don't think my local/online shopping habits would change just to save 3% on taxes.