If you've ever worked with a group of people you should be able to relate to this.
Something that has taken me 30 years to figure out about "brainstorming:"
It is favored by groups with no accountability.
"Brainstorming" is such a touchy-feely process. It's used to promote inclusion amongst a group of disparate people who probably shouldn't be a group in the first place. It's used to come up with ideas that cannot be tested or otherwise iteratively developed prior to deployment. It's a way for everybody to contribute to the process, regardless of whether or not they have any justification to contribute to the process or not.
Classic brainstorming - gather everyone around the conference room in order to come up with advertising ideas for the company.
Traditionally thinking, "brainstorming" permits the introduction of ideas from outside normal channels and puts creativity at the forefront. Realistically speaking, "brainstorming" eliminates expertise, promotes lay thinking, insults those who know what they're doing and patronizes those who don't.
Maybe you're an engineering firm with three departments of four engineers each. You have a drafting pool of 8 guys. You've got an accountant, you've got an HR person, you've got a receptionist. Your 12 engineers know fuckall about advertising and don't want to. Yet here they are, shouting out bullshit because they're required to be. Your HR person knows AFLAC and COBRA and doesn't want any part of this. Your receptionist at least went to art school, but here, in this one corner of the world where she's actually got more expertise than the people whose asses she wipes all day, she's relegated to "equal." By sheer number you end up with a bunch of ideas that the engineers come up with, that by concensus, are favored 12:1 over whatever the receptionist comes up with. Ta daa: bad ideas run rampant.
Let's suppose instead of burning half an hour (at an average of $150 billable per: that's over $2000 just for this little sit-down) you send out an email to anybody who has ever shown anything like a creative side and put them on a small group whose job it is to evaluate - wait for it - $1000 worth of advertising research by a firm that does advertising for a living. Now nobody's pissed off, the people who want input are enrolled, and you get a quality product without churning your wheels.
FUCK brainstorming.
Interestingly enough, here's what "brainstorming" looks like when there's some accountability at the end of the process: