Most of the middle class society won't be able to do that. Only when you have a lot of capital that you can invest into bitcoin without any risk, and with advanced trading knowledge, only with these things along with investment of time, you will be able to earn a good stable income which will be enough to stabilize you without any field job.
Also, bitcoin is very volatile and not accepted that widely, so many people won't have the courage to earn the whole of their livelihood in such kind of a currency, whose value may be zero within days, and when they won't even be able to use that much.