Bronk, I think you might have it backwards.  As long as someone is providing thier opinion while staying in the realm of thier knowledge, then they are making a potentially qualified opinion.
I say 'potentially', as the basis or knowledge drawn on to make the opinion can be flawed.
There have been people on this board who state things in a manner to lead you to believe they are experts in the field.  Then later on, you find they are anything but experts.  They usually tip thier hand when confronted with a fact, they presume to be an opinion.
Fortunately, most people stay within thier realm of knowledge, for the most part.  And that usually can lead to a fair exchange of ideas and opinions, where everyone learns something.