I don't understand how these coins have value. Surely things only have value if they:

1) have some scarcity, and 2) have some useful purpose.

I can see how these coins get scarcity, but what is their useful purpose? What can I do with FacebookKillerCoin or TwitterKillerCoin or EAGamesKillerCoin? If they're just essentially 'gift card currency' and the company will buy them off me in exchange for their products, why use a blockchain in the first place? Just call them loyalty points or whatever.