Depends where they got the opinion. If it's something that most people have experienced then they probably have a pretty grounded opinion but if its something they're only aware of because of news then there's reason for skepticism. Ask people on the street their opinions on something related to the economy and its a mess.
Opinions can easily be based on ignorance, copycat behavior, group pressure, is a product of that time, etc. Even experience can be a wrong basis for an opinion