The even greater fool theory is thinking that you’re somehow contributing to a better world by buying stocks on a secondary market (e.g. exchange)
The only thing that can be considered “investment” is VC capital or new issues of shares (e.g. IPO’s). If your funds are not directly contributing to projects or new production, it is speculation.
Note: I am a massive BTC bull, just pointing out that alot of what Gates would call investment is also not investment by his own philosophy