No I don't think it's stupid, people who invest in Bitcoin also invest in other assets like gold, silver, stocks and other things that could make them profit in future.
It's much more stupid to invest your money in bunch of shitcoins, ICO's and in worthless NFT monkeys and silly pictures like that, but people are still doing this.
I am not big fan of stocks, but people can do whatever they want with their own money, and I think I saw FTX have some kind of stocks options in their exchange.