A stock represents a percent ownership in a company so it is backed by whatever physical assets the company owns along with the net income it produces. Stocks valued much higher than those things are a real gamble. A gamble that the company is really going to be worth more in the future. Many stocks are way overvalued but they are backed by more than "faith" (usually).
Dollars and most fiat currencies are backed by taxes. You must pay your taxes in fiat. Whether that's enough to really support the value it has is another question. Heck, by law every crypto transaction results in demand for USD to pay taxes. Other than that, yes, it is pure faith.
With cryptocurrency, it really varies. Some of it is purely faith (bitcoin for example). Other blockchains have real applications built on them that have value based on the demand for those services. However, separating actual value from speculation can be almost impossible. (Most) crypto isn't a scam but it is quite speculative.