In the case of Amazon there's a clear protectionist argument to be made. It will kill local businesses and send a bigger share of the profit to an American company. Replace jobs in those small independent businesses by underpaid corporate jobs at Walmart 2.0. Amazon is in a position where it can sell items at a loss for years just for the sake of killing small competitors. Granted, maybe it's the role of antitrust laws to take care of that rather than taxes, but I'm generally in favor of slowing down Amazon, if only to give other players a chance to grow before Amazon takes everything. The problem with antitrust laws is that they will come and slap Bezos with a tiny fine 3 years after Amazon has unfairly killed competitors.

If you want to tax and regulate Facebook, etc., I think the argument is much less clear, especially if those regulations are just going to cement Facebook's position against possible newcomers.