I think this reasoning is mistaken. Yes, bitcoin-accepting vendors act as a new sink for supply, but for that reason they also increase the incentive to leave b

I think this reasoning is mistaken. Yes, bitcoin-accepting vendors act as a new sink for supply, but for that reason they also increase the incentive to leave bitcoin sitting in your wallet, ready to spend on something you would like to buy (much as we keep money in our checking accounts so we can draw on them at will). In aggregate, if (big if) lots of people are using bitcoin as money, then speculative demand may decrease, but currency demand could increase dramatically.