You cannot reason them out of their beliefs. The BEST thing you can do is to work towards structure that will not permit the GroupThink, but allow them to be isolated, finally confronted with the reality that they have been programmed, and re-built into Homo Sapiens – THINKING Man/Woman.
We should look to ‘de-programmers’ who work with families that want to break their relatives out of cults. Other than just waiting until the cult collapses (often destroying their members in the process), I can’t think of another way to deal with it. A few will leave the cult’s intertwined social structure – for a job, for personal/health reasons, to move to another part of the country or to a more rural environment – and, sometimes, in the process, break the spell. The current situation, where people are leaving their urban environments for a less crowded environment, some are adopting the virtual lifestyle for work/school, or otherwise breaking free of the Omnipresent Borg, may be a stepping stone.
We need to follow that suggestion to set up Welcome Wagon committees, that will work to integrate them into their new lives. They need help to do so.