“But now let’s say some guy bought 100 shares of some old company like Coca Cola or Ford. A year later he sells those shares for a profit. That particular investment really did nothing to help the country.”
It does.
The market for shares is why people invest capital.
The market provides liquidity, which encourages capital formation.
The old guy who buys 100 shares of Coca Cola is a shareholder, having exchanged money for ownership.
Capital gains get taxed differently because they are the foundation of building wealth. It dates back to the New Deal, and Joe Kennedy Sr didn’t want to live in a society where his progeny would have to worry about keeping up with the “Joneses.”