Currently these giants have to pay less than bricks-and-mortar retailers[1], which is why the system is unfair. Amazon pays less taxes on a book sold than a small 1-person shop across the street. Until very recently, they didn't pay taxes in some countries at all [2]

[1] http://www.sueddeutsche.de/wirtschaft/steueroase-luxemburg-a...

[2] http://www.sueddeutsche.de/news/politik/eu-amazon-zahlt-jetz...