When the only thing backing up your currency is the belief that it can become stronger than the USD in mainstream society with no form of legal protection for your funds while simultaneously the majority of holders are buying and selling solely to make more USD, that is not quite a paradox but awfully naive.
I own bitcoins therefore have a part in 'backing up' the currency. Whilst I acknowledge the possibility (however remote) that it could become stronger than the USD this does not in any way have a part to play in my decision to own bitcoin, nor in my possibly mistaken belief that it is likely to have a more significant role to play than it does today.
So the premise that 'the only thing backing up the currency is [belief x]' has been proven to be a false one given that I don't back up the currency due to 'belief x'. This renders the remainder of your point irrelevant.