It raises an interesting point that if we spend Bitcoin to buy stuff, the companies will most likely sell the BTC pretty quickly.
What's wrong with that? Money just changes hands, from the customer to another one that buys them from the store. Even if it was destroyed, it would just make the rest of the supply more valuable. Being able to use bitcoins in as many places as possible, and as easy as possible, is what makes it valuable. If everyone just kept their coins, its purchasing power would plummet.