Stock is part ownership in a company, and comes with voting rights and dividends. It has intrinsic value. If you stop trading, and merely hold onto your stock, you still retain the voting rights and still receive dividends.
Bitcoin, on the other hand, does have no intrinsic value, and is a fiat currency. Fiat currencies are based only on belief in the system issuing them. Consider the US dollar, and the effect of the economic condition of the US on the perceived value of the dollar; or the Euro and the situation in Greece coupled with the cooling attitude of Germany towards the currency. The Euro could collapse if Germany pulls out and other countries lose faith in it as a viable currency.
Bitcoins are based on faith in the system that operates the bitcoin economy.
The EFF has declared a lack of faith in that system, in particular, that the legal foundation for it has not been tested, and the potential risk of being a test case outweighs any other value bitcoins may have.