As far as I know, bitcoin futures does not affect bitcoin price directly. When you buy buy futures, you can go short or long on bitcoin futures, and by that you expect the price to go down or up respectively, in order for you to have a profit (but you are not buying or selling bitcoin).

The "problem" with futures, is that you can now win money if the bitcoin price goes down. What everyone is saying" is that there is a great opportunity to buy bitcoin before the futures goes live, and by doing this you are making it's price go up (specially if you are a whale, like the Wall Street guys are). When futures go live, those guys can just short bitcoin, and at the same time sell the bitcoins they've bought before the futures went live. Since they have plenty of money, they might be able to have some influence on the bitcoin price, so by selling coins, they will be winning on the short they did on futures, and will cash out some profit out of the bitcoin sale as well.

After this they can go long on bitcoin futures, and at the same time buy bitcoin that is now at a shorter price, and again win on both sides. Of course this is not that linear, and the market will still be unpredictable, but this is a possible set up made by Wall Street whales, and this might be a way for the futures market to influence bitcoin price.