The idea that internet retailers have an advantage over brick and mortar stores is a fallacy. The online stores can charge less, and not charge tax. What they can't do is allow the customer to examine the item. They don't incur the shipping costs that online merchants do, nor do they have to eat many costs from returns and fraud that online retailers do. They also have the sense of trust, just by their presence, that online retailers have to struggle to create and maintain.
There are advantages and disadvantages for both types of retailers. Politicians are just looking for new sources of revenue. What they'll do is shrink their revenue base, as small online retailers like me won't be able to afford the extra accounting costs to keep up with paying taxes to all states.
With this kind of mentality, I'm surprised that government didn't require car owners in the early 1900's to use a horse and buggy at least three days a week, just to be fair to horse stables and buggy makers.