Since PayPal customers buying Bitcoin in anticipation of using it to fund future purchases must sell Bitcoin to buy an actual currency to transact with merchants, today's buyers are tomorrows sellers. If speculative fever dies down, who will take the other side of those trades?
PayPal's foray into Bitcoin is a gimmick designed to provide a short-term boost to Bitcoin's price. If PayPal really wanted to offer its customers an alternative and reliable long-term store of value, it could have allowed them to buy gold and store it to fund future purchases.
