In general, the people are already bitterly facing the huge problems brought by the current monetary system. If Bitcoin will one day dominate the world, there'll be disruptions which might be interpreted as sheer havoc wreaked by Bitcoin, especially by its critics. The truth is that these will be minor ones as compared to the continuous damage caused by fiat. And these are necessary, too. But we surely won't be crying a river when the money printer operator would finally lose his/her job.
1. When virtual currency or crypto-currency reigns all over the world, the banking system will be miserable, and a group of people (who do not know about crypto-currency or bitcoin) will be unemployed all over the world, who till now were working at the convenience of various banks.
I think the banks won't go. Their roles may significantly change, though. Custodians will never be completely erased from the face of the earth. Plus there are also banking services that Bitcoin might not be able to replace. But, again, that the staff of banks will have to move jobs because of Bitcoin is never a heavy toll as compared to sticking with the status quo in which the people's currency is devalued nonstop.
2: Unemployed people (due to a lack of knowledge of currency requirements or benefits) will not be able to handle this shock in the first place, due to which they will face various financial, lateral, physical, and mental problems, which is a big challenge for them.
Don't liken Bitcoin adoption to a bomb dropped from the sky. Why would people be surprised when the growth of Bitcoin is gradual? Right now, we're heading that way already. This has been going on since Bitcoin came into existence. It has been 14 years already. So, why would they be shocked when Bitcoin reaches a certain level of success? Bitcoin is a movement.
3: Many developing or underdeveloped countries (especially those with low leverage) will consider cryptocurrency a curse rather than a blessing due to their lack of proper understanding of its importance.
Lack of understanding is easy to address. They only have to spare some time learning about it. Governments must have already heard about Bitcoin. They can easily invite experts to provide them better enlightenment. What's hard to address is stubbornly sticking to the fiat standard despite fully knowing how damaging and poor of a monetary system it is. The only way governments are closed-minded is when their leaders are benefiting so much from a rotten currency.
4: I have seen among my acquaintances who still cannot fully trust the bank (banking is some kind of rigging or fraud) and therefore leave their valuable assets (gold or money) on their own instead of depositing them in the bank. For those who do not believe in banks, how exactly will they accept this currency system?
Gold and cash may be good but hard to keep. Moreover, they can easily be seized or stolen. They can also be damaged in many ways. They can't easily be moved anywhere, especially across international borders. They can easily be confiscated as well. As to cash, it might be replaced with a digital version sooner or later. As to gold, it can't be used as a currency. In which case, Bitcoin is much much better.