Market-makers gain profit from the bid-ask spread. This means that they could place speculative positions without any cost (they pay the spread to themselves = zero cost). I assume there are laws preventing it because if it could happen, the opportunities are far from equal for each speculative trader (I have to overcome the spread while others can trade spread-free).
My question in a more concrete way: how many percent of the 7 trillion daily volume in the forex markets is this "spread-free" volume? Can I be sure that some actor paid the spread to another for 100% of the volume, or is there volume that is somehow "spread-free" (I described previously)? Do larger independent actors (e.g. hedge funds, pension funds) pay the full spread, or can they get a discount on it?