The theory of comparative advantage ( https://en.wikipedia.org/wiki/Comparative_advantage ) tells us that optimal production requires exchange. If you prohibited the exchange of existing assets, it would not be possible to achieve the same total production regardless of who you assigned to produce what. (You could of course have everyone keep producing what they were producing for the trade-is-possible world, but if you did that, nearly 100% of all production would be thrown away as waste. Coal is valuable in small quantities as a heat source, but it's valuable to power plants only because they can sell electricity, and it's valuable to mine owners only because they can sell it to power plants.)

That is value directly created by exchange.

Roughly -- The value of an asset depends on who can use it.

When two parties agree to an exchange, it suggests that they both valued what they ended up with more than what they started with.

This assumption breaks down for most financial assets. Both parties still think that they are gaining value, but one of them has to be wrong.

This is completely wrong. I sell stocks because I need cash. I make a loan because someone else needs cash. Liquidity preferences matter, volatility preferences matter, both parties can gain value.