The government will always be the biggest threat to Bitcoin because they have the power to ban it. Look at China and how they banned any cryptocurrency from being traded if all governments decided to ban Bitcoin then it would be very difficult to trade Bitcoin to fiat I would say unless you are buying Bitcoin with cash it would be impossible since the government could track it. Even if cash to Bitcoin was possible most people would not want to do it because they would have to reveal their identity and there are other security risks when dealing in person. I think most people including me would stop using Bitcoin if it was made illegal.