If you create an ad on television stating that you are buying tons of a particular model and make of car, and then demand for that car goes up, why is this seen

If you create an ad on television stating that you are buying tons of a particular model and make of car, and then demand for that car goes up, why is this seen as a negative in a functioning economy? A functioning economy responds to demand. Now what is the difference between sending an exchange an order for more shares than they have available and a television ad broadcasting your buying intent? In this day and age: not much. What isn't happening: small traders, like you and I, are not sending small trades to markets and having them be "intercepted" by HFTs. HFT's wouldn't pay attention to the "guy buying one car" type of trader, and there isn't enough of a difference in the signal (your trade) and the current market price to be arbitrageable.