Your theory only works with a perfectly efficient market. In practice, even without commissions, there are many other sources of inefficiency in the market that

Your theory only works with a perfectly efficient market. In practice, even without commissions, there are many other sources of inefficiency in the market that act to reduce your returns every time you trade. The bid/ask spread is an example of such an inefficiency. Take a hypothetical case where you just buy and sell the exact same stock over and over, but the price of the stock never changes. Every time you complete a bid or sell order, you would lose an amount equal to the gap between the bid and ask prices. Repeat the cycle enough times, and you will lose all your money, but the stock price will never have changed. What's the opposite of this strategy? To never trade at all? The idea that you can just reverse a losing trading strategy to come up with a winning strategy is absurd, because it completely disregards the entropy inherent to an inefficient system.