Or it could do better -- dispense predictions/instructions so as to ensure an even distribution of traffic (e.g. by randomization).
The system actually requires itself to be ethical. The ability to make things better for the paying users is dependant on the system having a lot of free users. Those free users have to be getting some utility out of the site, otherwise they won't use it. And without large numbers of free users, the paying services can't be offered!