I don't think everything is opinion. If common understanding of the premises of a question is close enough, there are definitely right and wrong answers. That being said, one could argue that the spectrum of how close an understanding of a particular concept that two people hold is infinite.

I don't think everything is necessarily opinion. If two people have a close enough understanding of the premises of an argument/question, there definitely can be definitively right and wrong answers. That being said, one could argue that the spectrum conceptual synonymy is infinite.