I also found this article about the Mandaeans in Massachusetts:
https://www.pri.org/stories/2016-10-06/these-iraqi-immigrant...
https://www.pri.org/stories/2016-10-06/these-iraqi-immigrant...
That’s interesting. Seems like the religion is “doomed” to forever remain that of a small and shrinking minority.
"Mandaeans believe in marriage and procreation"
But this article speaks precisely to your statment: http://articles.chicagotribune.com/2008-11-16/news/081116007...
Also, the edict is only since 1937, they were accepting converts earlier than that. So fundamentally they aren't a success story - they haven't been doing this very long.
Other Jews can marry in, but even this is limited. The majority of self-identifying Jews in the US would not have the qualifications to marry in. Any how, they are an insular community.