Those are what I call BUT meetings. "But" is another word for NO.
When I facilitate a meeting, we deploy a tool taken from the world of improv theatre. It is the use of the word AND.
When someone begins a sentence with WHAT IF? and after they articulate their idea, then the next person has to begin their input with "AND".
The premise is that with "and", you can't help but build on the idea.
The goal is to get the "What if" ideas out on the table and to get people thinking Why Not? And being willing to say, let's just DO IT!