This is how I think futures affects the price. Someone please correct me if I'm wrong.
Say in November bitcoin is $8k, and Bob bets that in 1 month time that the price will be $10k. John agrees to the futures and to sell bitcoin at $10k to Bob in Dec.
In December, the bitcoin price is actually $15k. Now Bob gets a $5k discount, and John loses $5k - plus a whole bunch of bitcoin is sold at $10k when the price is $15k.
Does the whole market react and then tank because a whole amount of bitcoin was sold at $10k??
That would be correct if it required physicl delivery, but this is a cash settlement system, so no Bitcoins are involved.