There are a lot of reasons regarding people fear about bitcoin:
1. Bitcoin is in it's development stages yet.
2. Digital currencies are new technology and most of peoples are unaware of it's actual definition.
3. People fear to invest in it because they are used to paper money and they think that it digital currency is not permanent and may end any time and their investment would go in loss.
4. Some people think that it might be a spam.
5. It is uncontrolled because it's price varies time to time.
6. People think it is not authenticated and have security issues.
7. Many governments have banned it, and labelled it as illegal.