Yeah, it is a free service to sky subscribers.....if you do not subscribe to Sky Sports then you get the relevant subscription reduction....the same is not true of Sky Go you get it free if you subscribe to any Sky package, it isn't part of a fee package itself....thus it is a free service to all sky subscribers.
It is like going into a supermarket, buying a Sausage roll and getting another one free.....the cost remain the same whether you take the free sausage roll or not.
In any case the service has terms and conditions that are plainly laid out.....the OP accepted them and tbh, he is blowing it all out of proportion.