The problems with crypto-currencies being widely adopted are the same as the benefits. While people who understand the benefits like it, the same could be said for cash, which is widely going away and had far better adoption.

1. Loss aversion - You lose your bitcoin wallet you lose everything. You can't have that with large amounts of money or you'll bankrupt people.

2. Anonymity - Thieves can steal money, and to get it back you have to expose yourself and claim the money, if you're lucky enough to get it back at all. Governments can also very easily track users.

3. Decentralized - You have no one single person to punish when things go wrong, or seek help from. You're alone just like everyone else.