In a nutshell, i think big banks (and their lobbying power), and governments are the biggest threats to Bitcoin. We know that they can't stop BTC, but that can make it harder and harder to grow and use if they lay the hammer down as hard as they can.
I think most of us can agree that we want each BTC to be worth as much as possible, and govts and big banks can have the largest influence on preventing that from happening.
IMO , at best they can only don't recognize bitcoin but they can't ban it .
Banks don't like bitcoin cos they can't tax it ?