Bitcoin is an alternative medium of exchange and to be an effective medium of exchange, it must be acceptable in exchange for goods and services. Bitcoin's use is still limited because only few stores or shops are accepting it worldwide compares to the fiat. But bitcoin can be used by people who want to avoid banks and other transactions that requires third party or middlemen. Bitcoin's economic function differs from fiat because it does not involve any government interventions.
Now there are more than just a "few" places where you can spend bitcoins, every year there are more and more places.
Effective medium of exchange is a trust between two or more parties, confidence in fiat system is lost a long time ago, now question is whom will you believe more: in bankers and governments or algorithm? Do you trust people or math? Bitcoin is a tool that can help economy to evolve, on local and global level. Transparency is one of the functions that bitcoin can offer to us. For how long we will live in the dark while rich people are getting richer with help from the governments and banks?