That "someone" doesn't have to be another crypto investor.

IFF it becomes a stable coin whose chance is almost nil in most of the countries.

But it's not nil, is it? From a future value perspective, that chance means that the entire market can increase in value, much like the stock market.

I'd also point out that as long as more people are buying crypto, the value can continue to rise (as there's more people purchasing crypto every day). That does mean that at some point people will lose, but in the short to medium term, buying today could see increases for a while.

All crypto isn't equal either. There are plenty of coins with more usability than others, both as a currency and as the base for other technical projects. Ethereum in particular is super interesting because of the smart contracts feature. A coin doesn't have to become a worldwide stablecoin to increase in usability and value.