More brains can be brought together
With more people contributing a wider range of knowledge and perspectives can be obtained. Even if "stupid" questions are asked, these may be sufficient to prompt others to ask better formed questions.
The debate can be described as a participative process as many different actors are involved. However, most participants do not have a broad and comprehensive view of the problem. In other words, each participant has its own vision of the problem, and its own knowledge and information. Once confronted to other opinions, arguments, results the participant may realise that is not exactly what it has expected. So he can add new or revised knowledge, rule, values, preferences, etc. during the process.