Given the infinite number of possible alternatives available, the only way that uniformity in belief systems, regarding aspects of reality not subject to rigorous scientific experimentation, is attained is through conversion by dominant individuals or groups of submissive individuals or groups. Uniformity of some degree is essential to provide common goals and purposes and harmony of activity within a society. So the effort to provide uniformity has utilitarian components, though it usually also contains components that serve more the interests of the dominant individuals or groups.
Some attempts at conversion are arguably pure utilitarian, particularly with regard to certain interpretations of utilitarianism. For example, spreading the belief that long-term benefits should be prioritized over short-term benefits would be purely utilitarian if utilitarianism is interpreted to mean “the greatest good for the greatest number over the long term.” So the conversion of others to this belief could be characterized as purely utilitarian.
However, this example illustrates how no conversion, or motive behind a conversion, can be critically reviewed except with regard to particular goals, and the goals are arrived at by a priori desires
One other point is that those converting others to prioritize long-term benefits are more likely to create a sustainable group or society than those converting others to prioritize short-term benefits. The latter groups usually vanish from the face of the earth in the long-term and we are left with the former groups.