Allow me to address some of these concerns.
First, there tends to be a theme of "Actually the banking system takes my money so I don't have to worry about securing it, so it's cool." Which is fine to some degree, but as a poster above said, there's nothing preventing banks from holding onto your Bitcoins or other crypto for you in case you would prefer that method. Hell, there's a crypto exchange right now,
coinbase, that operates on a principle of holding your bitcoins for you because you don't want to be bothered with the process of holding your own funds. So it's a bank, as long as you trust it. It's even
FDIC Insured if you keep your money in their system denoted in USD.
Plenty of people, myself included, are willing to take the risk on holding our own funds because most of us are growing tired of trusting the same banking system that caused the housing collapse in 2008, and can see the writing on the wall when you look at the economies of countries like Greece and Venezuela and think that we can't be vulnerable to the same shit.
So now to address the points individually.
There have been many advances in the technology surrounding Bitcoin and Cryptocurrencies to defend against that. Most notably will be
BIP32 and
BIP39 respectively. It took me quite awhile to see how they actually work, but for Joe Blow here's what they boil down to: You don't need to actually store coins on a computer. If you can remember -- or more realistically, write down on a sheet of paper/tattoo/stainless steel and secure in any fashion you like -- between 12 to 24 randomly selected English words, you will not lose your coins due to any electronic catastrophe. Simply pull up any BIP39-compatible wallet software (and any wallet software worth the code it's written in will be BIP39-compatible) and plug in your 24 words, and boom, you're back up and running with your fully restored wallet.
If you're referring to existing data getting corrupted, the fact that at least the bitcoin blockchain's data is massively distributed, and constantly checked against for corruption at all times by any full node that fires up defends against that possibility. If any one full node suddenly looks significantly different from the other full nodes, they will no longer be compatible with the network, and will be summarily rejected.
As for the possibility that something in the future will corrupt new bitcoin data or processes, and as such prevent new records being created. That, I'll grant you, given that the Segwit2x fork attempted a major change and ended up stalling out by an off-by-one error. That's a legitimate concern that people will have to be very careful of for any future changes to code, processes, or potential new DLT's that pop up with their own coins that want to unseat Bitcoin.
There is a certain amount of faith I put in Bitcoin in particular because they play very conservative when it comes to major network changes as it will help prevent problems like that, among other things.
My answer to this will be along the lines of "an ounce of prevention". People have been learning how to secure their cryptocurrencies from theft using some genuinely interesting techniques.
- Storing coins across multiple wallets, each with different security models. See this video by Andreas regarding how he stores his coins -- all the way from "cold storage" to daily operating cash. If one of these wallets gets compromised, it's not ALL your coins.
- Duress Wallets, so that if you're theoretically mugged you can give someone a fake password that gives your assailant access to only a small amount of coins. Many wallets are beginning to implement "passphrase" features to facilitate this, and it's especially popular among hardware wallets. Speaking of...
- Using dedicated hardware wallets, to prevent coin loss in the event of a hacked computer. These store your coins in a way that never touches the internet. All transactions are signed on the device itself, and thus your private keys never touch a networked computer.
- Then you run into shit like the Glacier Protocol which is crazy and takes into account every possible way these people can conceive of in which your wallet can be compromised.
I'll be brief with your second list.
This is just reiterating, but this assumes you either store your coins in a single wallet, or in a singularly compromisable (if that's a term that makes sense) location. The fact that you have to take responsibility for securing your own liquid funds doesn't mean people aren't willing to take that responsibility, and as outlined above, people are willing to take that responsibility very seriously. Plenty of people can be, will be, and have been burned by not sufficiently being aware that coin storage is a real responsibility in the crypto space. Hopefully that lesson doesn't have to be re-learned too many more times by people.
I gave you the possible scenario of blockchain network itself becoming non-functioning in a way where new transactions cannot be made. That's legitimate to a degree. The other scenario that covers your situation is a global electronics blackout, and if that happens, then you will have much bigger issues than "Does the bank have sufficient records that I have X balance on my account?"
See the above paragraph where I mention Coinbase and the possibility of other such crypto-based institutions to exist.
If you have any other questions, I'd love to try and help answer.
