In the context of a graded quiz, multiple choice questions must have right answer(s). Here are a few alternatives.
If you are using the New Quizzes quiz engine, there are a couple approaches to cause any answer to be marked right in this thread (I'm not sure how the varied points solution will behave when zero points are possible) :
How to accept any answer as correct in multiple choice questions?
If you are using the Classic Quizzes quiz engine, you might make these questions essay questions. That will prevent Canvas from marking them wrong when the student submits the quiz. It will also say the quiz submissions need grading, so you would need to open them in SpeedGrader and click "Update Scores" for each student.
You could also separate the opinion questions into a Classic Quizzes survey that is due at the same time as the graded quiz. Students could do one, then the other. (With sequential module requirements, you could require students to attempt the survey before starting the quiz.)
How do I add requirements to a module?
