I am open to the option that my brain has the saved the wrong definition on opinion, but

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http://dictionary.reference.com/browse/opinion
noun
1.
a belief or judgment that rests on grounds insufficient to produce complete certainty.
2.
a personal view, attitude, or appraisal.
3.
the formal expression of a professional judgment:
to ask for a second medical opinion.
4.
Law. the formal statement by a judge or court of the reasoning and the principles of law used in reaching a decision of a case.
5.
a judgment or estimate of a person or thing with respect to character, merit, etc.:
to forfeit someone's good opinion.
6.
a favorable estimate; esteem:
I haven't much of an opinion of him.


http://www.merriam-webster.com/dictionary/opinion
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Full Definition of OPINION

1
a : a view, judgment, or appraisal formed in the mind about a particular matter
b : approval, esteem
2
a : belief stronger than impression and less strong than positive knowledge
b : a generally held view
3
a : a formal expression of judgment or advice by an expert
b : the formal expression (as by a judge, court, or referee) of the legal reasons and principles upon which a legal decision is based


I can not find a source that would support the claim that it would be a requirement to be not verifiable for an opinion.