unlikely. i think it has more to do with competitive pressures in markets and the elimination of a lot of the less sophisticated participants (partly due to higher frequency trading).
While that is true, the guy who said it was unlikely was guilty of the same crime. They both need a "citation needed" response.
I personally remember enough cases like Steven A Cohen and Galleon and the Gerson-Lehrman group[0], that I assign the probability "likely" to that claim, so if someone says "unlikely" I ask him for his reasoning because I might need to update my estimates. I was not trying to say it is wrong, just understand his reasoning.