Is financial speculation ethical according to Buddhism?

Imagine someone buys money in foreign currency, then sells it at a profit. Does Buddhism consider such operations ethical? Note: One possible reason why it may be unethical is the purpose of money -- to facilitate the exchange of products and services. When money becomes subject of trade, it cannot fulfill it main function and this hurts other people. Money to the economy is like blood to human body -- the more blood you remove from the body, the worse it will function.