If your son was not once a witless, chances are that someone did a damn good job of scamming or terrifying him that he would die soon unless he became a witless and then getting him to believe his family is evil.  That is the trademark of the witlesses.  If he was physically kidnapped and was never a witless, I would suspect either another cult with more physical barriers or some other criminal activity.

If he was a witless, there is a better chance.  If he is single, reasonably intelligent, no prospects, and no family in the cancer, then I wouldn't put some of the hounders above kidnapping (any more than I would put them above protecting pedophiles).  This is not something the Filthful and Disgraceful Slavebugger encourages--however, it is not beyond the realm of possibility that one of the hounders took it upon himself to "save" this "precious" life.  It should be reported to the police if you reasonably think this might be probable (either way, it needs to be reported at once).