In the product definition and design phase of product management the technique of improvisation should take priority over finding flaws with an idea. While responding to a person’s idea, the first step should be to build on the idea and make it better. This is particularly important when the team is building a product for the first time. Comedians and creative artists, particularly in the field of animation, rely on this method to create compelling experiences for their audiences. As a person who is very interested in building the best possible product, I suggest that the product manager should take on the leadership role and suggest that the team follows this methodology. It goes without saying that the product manager should practice this technique.
I am not suggesting that you agree with everything that your team members say. But first improve upon the idea proposed by a person and build on it. If the initial idea is not good enough or inappropriate, the idea will gradually fade away when better ideas come along. It is not a good use of time to jump and point out a flaw, when the purpose of the session is to create new things and come up with ideas. A good book on this topic is 'The Improvisation Edge" by Karen Hough.
When a you must point out a flaw in an idea it is better to follow the ‘Six Thinking Hats’ methodology created by Dr. Edward de Bono. The methodology provides a means for groups to think together more effectively, and a means to plan thinking processes in a detailed and cohesive way.
A simple way to use the “Six Thinking Hats” methodology is to clearly state that you are wearing a white hat while commenting on the positive aspects of an idea and clearly state that you are wearing a black hat before pointing out the flaws or gaps in the ideas proposed by others.