You're ignoring the fact that a customer buying from a business incurs an opportunity cost from other things they could have spent money on (or invested). In ad

You're ignoring the fact that a customer buying from a business incurs an opportunity cost from other things they could have spent money on (or invested). In addition, it merely shifts the money. If someone is thinking about getting Subway, but sees a McDonald's ad and goes there instead, that helps McDonald's but hurts Subway.