Sometimes cliches exist because any truth becomes trite when repeated enough. Sometimes, they exist so that people won’t notice the truth.
Reasonable people cannot disagree. This is clear if you give the matter some thought.
Either reason mandates a position, or it does not.
If reason mandates a position, then reasonable people are required to accept that position; to reject it would be unreasonable.
If reason does not mandate a position, then holding a position on the matter and expecting others to adopt or acknowledge it is unreasonable.
Reasonable people do not have to hold precisely the same positions on everything, most especially if the information available to them differs, but they can never disagree about any position. Disagreement indicates error on the part of at least one of the participants, possibly more.