Well, the individuals involved inside of the consensus process itself get to define what "rational" means.
In the methodology of non-dual consensus, "rational" is defined first as simply being honest. For example, if someone is to acknowledge they made a mistake, or do not know an answer; this is evidence of "rational" thinking.
Secondly, "rational" is defined like it is defined in economics, which is the ability to communicate what is in your own best interests without making a contradiction.
Thirdly, "rational" is defined by the ability to perceive and communicate what is in your best interests as well as the interests of those you are building a consensus process.
Over-politicized thinking is not your friend, and, thus "irrational" to use in consensus building!