"especially when that someone else doesn't take money from you. "
Power companies happily take money from you. And... power companies are regulated by the government. Arbitrarily shutting off your power at any time might not go down too well with regulators.
neya stated "This is why you should never build a startup/app based on someone else's API especially when that someone else doesn't take money from you."
I think you misread. He/she stated 'someone 1' = 'facebook itself' and that 'someone' takes nothing from 'someone 2', where 'someone 2' = 'developer'. Nowhere in that equation does 'someone' refer to 'facebook user'. In your example 'someone 1' = 'platform' and 'someone 2' = 'user'. These aren't the same.
Power companies happily take money from you. And... power companies are regulated by the government. Arbitrarily shutting off your power at any time might not go down too well with regulators.