What is the point of asking a question when you already know the answer?

I am referring to when a question is posted as a legitimate query for information and as responses come in the asking party then argues each post made pushing their obviously firm opinion on the subject.

I saw this again today and have seen it in the past and am just curious. (I no longer respond to these because it is a waste of effort)

How is this helpful?
What is the point?
What are they getting out of it?
Why are they wasting other users time?

I am not in the least grumpy about this. I just want to know why some people use a legit Q & A site this way when there is so much to learn and be gained by asking real questions.