I have seen many questions being voted for closure as being primarily opinion based. Now, if you think about it for a moment, aren't all questions opinion based (except the hard science questions of course)?
If there was one and only one correct (and legitimate) answer to a question, why don't we delete all the other answers once an answer is selected by OP? Take for example this question:
There are 12 answers to this question, with one marked as accepted. The accepted answer is at +36 score while the runner up questions have also scored +17, +15, +7 scores (the top 3 respectively).
Now considering that one answer has been accepted, shouldn't we delete all the remaining answers? Logically speaking, we should, because there is a question and there is an accepted answer to it. Keeping other answers intact would mean that we are consciously or unconsciously confusing anyone else browsing the site with a similar (or the same) question in mind. On the other hand, if only the accepted answer is available, it would provide the person with a direct, straightforward answer for his/her question.
Now I agree that this would be a very bad (and resembling a dictatorial society) practice because everyone has their own mind and someone with a similar (or the same) question in mind might find other answers more useful than the accepted answer. But the logical decision of a non-opinion-based society would be to delete all non-accepted answers for a question, since they represent nothing more than the opinions of the answerer-posters about the topic.
Maybe we should not shun opinion based questions. As it happens, everyone is unique and even questions marked hard science get different answers (logically speaking, only one answer should be voted up for such questions), many of which get voted up.
So I suggest that there should be an opinion-based tag available for question askers. Of course no-one is obliged to answer a particular question and knowing beforehand that the question is primarily opinion based would save the time and mental effort of all contributors.
Let there be idea generation and asking people's opinion about things. However I do admit that having a proliferation of such question may be detrimental to the core concept of the site. Opinion based question which are too broad or require too long answers can and should of course be discouraged and closed. However asking people's opinion about precise matters in short/medium length replies should be allowed.