1) Non-regulated form of money.
2) Highly volatile. A merchant will be discouraged to adopt a currency which is seen mostly speculatively.
3) Ignorance about the problems of the current financial system.
4) FUDs about the energy waste, criminal activity etc. (Which may also make them go against it)
5) It's difficult for them to understand the concept; it makes them give up on learning how it works.
1) We already have scriptural form of money. I don't think it's a big issue to add another layer for bitcoin. Some banks already adopt bitcoin or other altcoins, while some other businesses use paiement gates like Bipay.
2) It's just a matter of time until bitcoin reach a certain stability after solving the blockchain related obstacles. As time goes by, bitcoin will be less volatile, like all other form of value (gold,metal,etc).
3) This can be considered as a big problem for bitcoin in long term. If people won't be interested to change their attitude toward money ad monetary concepts in general, nothing can be done for short term.
4) FUD is also a matter of time as more companies adopt bitcoin in large scale.
5) I think this is the biggest issue but fortunetly we can handle it by spreading knowledge about Blockchain.