>XBT futures are cash-settled futures contracts that are based on the auction price of bitcoin in U.S. dollars on the Gemini Exchange. XBT futures are designed to reflect economic exposure related to the price of bitcoin. (http://cfe.cboe.com/products/bitcoin-qrg.pdf)
I think scam is a harsh word. One feature of trading futures is to hedge or "lock-in" in the price of btc. What this allows people who actually own bitcoin or accept it as payment, to reduce uncertainty in the price of it.
Apparently, to the best of my knowledge, when a transaction is initiated it, it queued in the network. You as a user have no control on what price the transaction will be cleared at.With futures, you can get more certain so that the price doesn't fluctuate wildly away from the agreed transaction price.
Where I think you are seeing it as scam, is that the futures are levered meaning someone can buy a bitcoin on margin, without having to put up the full notional/total value of the entire bitcoin, up front.