I don't see would-be evangelists as "preying on loneliness" so much as offering (from their point of view at least) a potential source of relief from it.

The JWs stopped bothering me after they discovered my taste for theological wrangling, and that I used their leaflets for textbook examples of fallacious argument. I got the impression though that their preaching is an end in itself, getting converts is irrelevant.

More recently I had a leaflet through my letterbox extolling the virtues of Islam. I wish I had met its deliverer: I'd have liked to invite them in for a chat as I could agree wholeheartedly with almost every point made.