Putting literally all your money into Bitcoin is not a good idea, not in a sense that you should buy some alts, but in a sense that you should have other investments and free cash. Rule #1 is to never invest what you can't afford to lose, and no one can afford to lose all their money.
I'd argue that having your money in fiat/cash isn't exactly great either. Look at the how much the inflation rates have increased recently. Plus, we're heading into one of the biggest recessions we've ever had, at least for a lot of people in their life time. Now, I probably expect Bitcoin to be effected just as much as fiat, but I'm not certain on that. What we do know is fiat will definitely be effected, and in a big way. Only have to look at previous recessions to find that out.
People won't be spending as much as they did a year ago, and that creates problems for an economy. People lose jobs, because their companies have ceased making a profit due to the reduction in spending from customers. It's a vicious cycle, which is likely to effect every currency out there. Bitcoin, in my eyes probably has the best chances of avoided issues.
However, I get what you're saying. Regardless of the way you look at it, fiat is probably going to be a lot more stable than Bitcoin, and investing all or a significant share of what you're worth, probably isn't the best idea, I'd agree. I do respect those that do though, kind of tells you they're very much sick of being a slave to society.