In this paper, we propose a computer-supported collaborative argumentation for the public debate. For this purpose, we use the Analytic Hierarchy Process (AHP), that can be viewed as an argumentation-based decision-making process, to help stakeholders to build an argumentation schema and to express preferences about it. Considering this multi-criteria decision-making as an argumentationbased decision-making, we construct a dialogue system of agents with reasoning abilities to support the group decision. Each user is assisted by an agent representing him in automated dialogues. Therefore, the system provides tools for the collaborative development of the argumentation schemas on one hand and to check the consistency or the inconsistency among preferences between two users allowing the conflicts and the consensus seeking on the other hand.