1 If the bitcoin becomes a bubble and burst. This will be linked to the flash crash but this time that looks impossible.
2 If the exchange site will be banned in the various country because of the exchange site as a centra key in the bitcoin or crypto.
3 Too many hackers, scammers in the crypto.
A lot of the things that makes me fear about the bitcoin itself. But the politic and regulatory seems to be a serious thing rather than other.
All of fears that you mention is same like the most fear is loss money.
I wil not explain more because people know why people not join in bitcoin and why many people still convinve their friwnd and family to not join here in bitcoin. All because the most fear is lossing money.