In a hierarchical system, those at lower levels may expect to have their say, but do not necessarily have any control over decisions. It has to be active participation, not rubber stamping preformed agendas. There has to be a chance to influence content, a say in the actual decision and the opportunity to dissent. Policy forums attract politically active members but are purely discussions. In particular, there is little mechanism for expressing alternative conclusions.
Pluralism is a key principle as well.
It is often important to have a dissenting minority either to prevent authoritarianism or to ensure the existence of more than one set of ideas which can contribute to problem solving. That is part of intelligent decision making. Having said that we have a value for consensus, as an end in itself, but one which has to work alongside other values such as intelligent decision making. The ensuing discussion centred on whether we should accept any exclusion at all in principle. However, one of the principles of intelligent decision making is that a decision system has to have more than one primary, anchoring value.