Almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so.

Heinlein’s remark is a warning about the political behavior of organized belief systems: once a group grounded in doctrine gains state power, it tends to convert private conviction into public compulsion. The target is less faith itself than the fusion of religious certainty with coercive authority—an impulse that can appear in mainstream religions, small sects, or quasi-religious ideological movements. The quote reflects a civil-libertarian concern for pluralism and church–state separation: laws should be justified in broadly shareable civic terms rather than enforced as orthodoxy. It also implies a structural lesson about power: incentives, not just theology, drive the urge to legislate creed.