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??