Social cohesion is a necessity, and mankind has never yet succeeded in enforcing cohesion by merely rational arguments.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“In changing forms, it has persisted down to the present day, and no doubt will persist for many ages to come. It is clear that each party to this dispute—as to all that persist through long periods of time—is partly right and partly wrong. Social cohesion is a necessity, and mankind has never yet succeeded in enforcing cohesion by merely rational arguments. Every community is exposed to two opposite dangers: ossification through too much discipline and reverence for tradition, on the one hand; on the other hand, dissolution, or subjection to foreign conquest, through the growth of an individualism and personal independence that makes co-operation impossible.” source