Truth is subjective and it doesn't need to be actionable. You can believe that something is true but you can choose not to act on it, not to do something about it, or even not to share it. Agreement is necessary if you want to do something together. If there is a common goal - like living in prosperity and without violence on this planet - then people sharing that common goal need to agree on the key actions.

The fact that what they agree upon is the truth is disjunct from agreement itself. We can agree to live a lie or to live a truth, they're both possible, as long as there is a common, shared goal. Consensus is about agreement, not about truth.