One of the fears here seems to be that there has been quite a bit of theft of bitcoin (et. al.). The problem with this argument is that anytime there was any theft, it was from an exchange, rather than from a wallet. Essentially, it's impossible to hack the currency itself, so if you do things like cold wallets, the currency is very safe. But if you keep a large amount in an account at an exchange where if the exchange is hacked you lose your money, then you're doing it wrong.
The exchanges originally were specifically designed to be a clearing house so that if you wanted to legitimately exchange from one currency to another, you'd simply take the money out of your secure wallet put it in the exchange account, make the trade, then put it back in your own wallet. And by virtue of it all being digital, it was supposed to be super efficient and cheap to do... compared to a forex exchange at least.
But if you're dealing strictly with one currency, you can much more easily protect your cash. When I first got into it, I had a sheet printed (done cold and off the internet completely) that had 10 or so wallets printed on it... anytime I would make a transaction, I'd send what I needed to, then empty that wallet into another one of the cold ones... essentially always having 2 trades and never keeping the money in the same place... basically impossible to hack.
It's an amazing technology, and if there were a way to invest in the blockchain technology somehow, that's where the real money will be!