You are only looking at the first layer of things. Did you know that someone that wants 100% safety in a portfolio needs to add stocks to it? I have run the numbers (backtesting going back to 1926), you cant just put 100% in T-Bills or T-Bonds, or gold. Its a balance between bills, bonds, gold and stocks that creates safety over different enviroments. So even though the person is adding volatility (stocks), risk is going down (risk being measure as something like CAGR/Max DD or the Sortino ratio).
Bitcoin is similar, we are talking about 2-3% of a balance sheet, not all cash (although, some will put way more than that). But if USD goes into the toilet, that 2-3% will be a life safer. If you dont have it, then you are fucked. So ironically, you DECREASE risk by adding.
Chamath said it best, BTC is insurance against the governments doing dumb shit. Its better to have insurance than not have it