Blind of Lies, you raise some pretty relevant questions about JWs and prosletyzing religions in general. These types of groups generally do not appeal to people who are just getting on with their lives and who are in loving stable family relationships.
In my opinion, people who are suffering significant pain would find the promise of a better place - whether it be heaven, earth or some other place - alluring. Consequently, JWs tend to attract people who are in some way suffering. Whether you call this exploitation is another question altogether. The Witnesses certainly do not get much monetary benefit from attracting mentally unwell individuals who, as a rule are more likely to be unemployed, probably already in considerable debt and have meagre sickness benefits.
JWs are no better or worse than other religions that 'play'on people's fears. In the mid 1980s I attended a couple of pentecostal revival meetings out of curiosity. In both, the same large number of societal down-and-outers went up on stage to have the pastor pray over them to release the bad spirit. In both cases, they left the revival just as troubled and in pain. Is that exploitation of people's vulnerability??
If mentally unwell individuals join the witnesses it would not take them too long to find that the witnesses do not have the promised answers. It's good also to kep in mind an incontrovertible fact: Although the path leading into the kingdom hall is narrow, the fire exit is huge: In some areas, those leaving the religion outnumber those joining.