Usually every brainstorming session ends up, at least in my experience, with a "vote" on the ideas generated. The vote is not substantiated by anything. No need to justify.
I fail to understand how voting for stuff (which is basically the dictatorship of the mainstream opinion) is going to get the most creative solutions on the table. That defeats the whole purpose, and makes brainstorming fail to deliver on its promises.
I have never experienced voting on the outcomes of a brainstorm session and that makes no sense at all to me. It's about generating ideas and it will, hopefully, include ideas that sound nice initially, but are bad when given some more thought. There should be a round to separate the wheat from the chaff.
In my experience (again), we do have two rounds to separate them. But both of them are voting-based rounds. One vote to narrow down the 30+ ideas to like 5 or so, and a second one to reduce it to one or two :) The outcome was very minimal compared to the overall time wasted on the process (5-6 people in a room, for one hour, ending up with a not-so-interesting idea... there are better ways to spend a team's time).
I see your point, but since "brainstorming" is used also in "design" environments, we are not always talking about efficiency here, but simply straying away from the too obvious ideas and avoid repeating the same old stuff again. I guess it really depends what you expect from the brainstorming session.
I fail to understand how voting for stuff (which is basically the dictatorship of the mainstream opinion) is going to get the most creative solutions on the table. That defeats the whole purpose, and makes brainstorming fail to deliver on its promises.