@Yog - I like your answer, however I fear we aren't addressing an important implication the Expansionists and others within the Wheel will be confronted by with and troubled by due to ghost immigration - if they have afterlives or reincarnation systems of their own, then why do ghosts exist and linger on?
This could probably be neatly explained (although correct me if I'm incorrect in my cosmological/metaphysical understanding about how and why ghosts form and persist) as resulting from these ghosts/spirits/souls, whether due to strong attachment to persevering the continuity of their ego/consciousness/soul/self, strong residual trauma, desires, or experiences they aren't ready to or don't want to move on and away from, lingering uncertainty as to the true fate that awaits them after death (or dislike/dissatisfaction in what they believe/suspect that fate to be) - these departed desire and would benefit from the certainty and security which the Wheel provides, wishing to experience more of life in a manner they can know with certainty is in many respects comparable to their own experience of existence and existing, while safe in the guarantee they cannot be cruelly nigh-randomly ripped away from such life again, and would only depart once more upon their own volition and terms.
Basically, explaining to the populace reasons why those outside the Wheel might wish to join it and would otherwise linger on in a often less than ideal proximation of their prior existence (ghosthood), and what cosmological "niche" the properties and characteristics of the Wheel fulfil for such people, as to reassure the Expansionists and other groups/movements/faiths/schools of thought that, at least to our own knowledge and understanding, the existence of such ghosts does not inherently imply that afterlives and/or reincarnation beyond the Wheel is horrifically dysfunctional, having "abandoned" these souls, or does not exist.