Quote from logic_man:
If I as a retail trader buy or sell a futures contract at a given point in time at price X, are you saying that someone with access to a non-exchange-based market can buy or sell that same (or an essentially similar) asset for less than X?
As a retail trader, "at a given point in time" you are buying/selling very low quantities. It's quite a different game when you need to move sufficient quantity that you'd be wiping out half the book if you tried to do it in one fell swoop. The simplistic retail notion of price doesn't hold there.
It should be obvious that once retail has something resembling direct access to the traditional exchanges, the real action is going to move elsewhere.