Um, what differentiates bitcoin from a stock on the open market (other than the technicalities, centralized vs decentralized)?
Stocks are just virtual pieces of paper saying you own X amount of something. So is bitcoin. Stocks are valued not by some formula, but by the constant battle between buyers and sellers. So is bitcoin.
The only real differences are that stocks are somewhat more protected (SEC and all that) and are not treated as property like bitcoin. I guess if you own enough stock you can steer the company you own to some degree, whereas with bitcoin the developers have more of a say than the holders.
Other than that, whether you like bitcoin or hate it, it has many more similarities to the stock market than differences, and anyone who spends their day in the stock market then turns and thumbs their nose at bitcoin seems a bit hypocritical.