I saw an expose of this group. It’s much more than you may think.
https://en.wikipedia.org/wiki/NXIVM
I read the article and it sounds like they controlled people with blackmail and finances. However the material for blackmail and financial docs were provided willingly by the victims themselves. They WANTED the cult to have absolute power over their lives because they themselves felt they lacked the discipline to live free.
Terrible way to take advantage of weak people but what exactly was illegal?