Previous political sciences research has revealed that democracy (democratic institutions, consultations with citizens) and technocracy (specialized knowledge of experts) are the main foundations for the development of effective and socially acceptable public policies, and that there should be balance as well as interaction and exchange of knowledge between them. However, there is a lack of e-participation platforms supporting this required `duality': the collection of policy related information, knowledge and opinions from both citizens and experts, as well as the communication and interaction between them. This paper contributes to filling this critical research gap. It describes the development of an innovative e-participation platform, which supports on one hand structured consultation and argumentation between experts/technocrats concerning important social problems and public policies for addressing them, and on the other hand the collection and interrelation of relevant citizens-generated textual content from numerous external social media. This platform enables the meaningful combination of technocrats' expertise with public opinion, allowing the technocrats participating in policy related structured consultations to retrieve, understand and get insights from citizens' perceptions. Evaluation results show that users appreciate the potential of exploiting the synergy of machine and human reasoning enabled by the proposed platform through a combination of data mining and structured consultation/argumentation - collaborative decision-making services.