The virus cannot steal large sums of money from the bank, you cannot just lose a large amount of fiat money - bank will not let this happen.
In fact, I find your thoughts strange to me, how do you say "you cannot just lose a large amount of fiat money - bank will not let this happen"? There are a lot of banks that have declared bankruptcy and people have lost a lot of money there without being able to do anything. You must remember the mortgage crisis in the United States in 2008. Many banks declared bankruptcy and the global economy was on the verge of collapse. The banks were closed and defaulted on their debts until the US government intervened to save the situation.
You can view the mortgage crisis here:
https://en.wikipedia.org/wiki/Subprime_mortgage_crisis
Choosing a place to store your money, you choose the type of criminals who will try to steal your money. Bitcoin will enable small fraudsters to steal huge amounts of money both in physical world and on internet.
if you have lost money as a private person, there is no problem. If bitcoin is scaled up to larger organizations, then the problem is already huge. Money and access to it must be protected and controlled by people, for this we invented banks.
If I were an organization, I would be afraid to use Bitcoin. I would be scared like of fire. I would like to sleep well, knowing that I am not responsible for protection of money. This idea is contrary to libertarianism, but Bitcoin is too harsh and cruel for most people.
Bitcoin is good not as a replacement for the fiat system, but as an ADDITIONAL mechanism to resist banks and censorship.