The latter. Futures do not change the supply or demand, and therefore do not change the overall results of a supply-demand curve. What they do is allow people to estimate where it will eventually land, and choose whether to lock in prices some distance in advance.
This ignores a subtlety. If one consumer locks in a large fraction of the supply at a low price, then the supply is smaller than expected, you've made the supply-demand problem more extreme for everyone else. So futures allow entities to lessen their own volatility, but that increases everyone else's volatility.