If Bitcoin is irreversible, they are useful for real life purchase since the merchants can save on fees, passing it down to the consumer. Bitcoin is way faster and have a lower fee compared to other methods of payment, making it ideal for long distance transfers. The only problem is with the spam, we just have to reach a consensus on that.
Now it's time for me to find these problems. What have you listed with real money? Can a simple person who does not have the knowledge in programming and cryptography to use crypto currency easily without coercion? It seems to us that everything will be fine but difficulties can not be avoided.
Simply bitcoin will not be used by majority of people in this world although we consider this as a global currency or whatever we call bitcoin to make it superior. It will remain as a payment system and as a payment system it will not work or will have no value with fiat as it's main currency.