Very important. Any memeplex that has aims that happen to produce kids will have a edge. It just so happens few if any secular memplexes have made this possible.

Another way a memeplex can succeed is by being very good at converting others. Note that such a memeplex if left unchecked could cause humans, or at least whatever culture it spreads in to evolve to extinction. As such leaders of other memeplexes may take extreme measures to suppress it.