Is it a good idea to organize a vote on a specific topic when you have already decided for yourself that you are certain about the outcome?
There’s a risk
This holds a certain risk. The risk that you get a response that is the exact opposite of what you expected. This makes the use of a voting system fun and exciting, but it can lead to pretty awkward situations.
So ask yourself first: ‘Am I willing to bear the consequences if the response to such a question is totally unexpected?’
If not, then it is probably wise to skip this question altogether and stay on the safe side.
What’s your intention?
On the other hand, it may be useful to take the risk in the following scenario: suppose that you are certain about how the majority of audience feels about something, but it is your intention to confront the audience with the fact that it is the general feeling.
You might want to do that because you suspect that they are not aware themselves, or to prove to a few dissidents that they are in the minority.
In that case, asking a question with a supposedly definite outcome can be useful to make something publicly visible, or to formalize an already assumed truth, but be aware that it always poses a risk.