It might take a bit longer than normal, but futures contracts make it a lot easier for whales to manipulate the market.
My take on this is the opposite. It reduces the influence of the existing whales by bringing a whole new set of players into the equation.
The new set of players could be people who never participated in BTC at all - futures contracts could make it much easier to short on a large scale for those who would rather not go on dodgy exchanges like Bitfinex.
The largest current BTC exchanges are still nowhere near the level of professionalism that most rich people who might want to try manipulating the market would expect.
It makes it easier to go long as well, but it was definitely harder to bet against the price of BTC rising than in favour of it before, and I expect futures contracts to change that at least.