There will only ever be 21 million units. As it spreads in adoption and use, it's value will increase massively.
It's a currency, and investment, a savings tool, a contract tool, it's all kinds of things.
It's NOT some currency a central bank and all it's managed henchman banks create at will, inflate the supply and give to their friends in secret. If you can't know the inputs (new units created), you must assume corruption. With dollars, who knows the endless ways they cheat. With bitcoin, we know in every block how many are created and if it was fair according to the protocol.