Why people find them so appealing?
I think we're in a very technical era, but human's mystical side can't be silenced that easy.
People use to need something to believe in (I'm looking for/ something to believe in, sang Joey Ramone). Many people use to feel empty in this strange but ridiculously monotonous world; I can't blame them. They're just everyday people, and day after day the world seems to be boring (not all the time, of course).
Then, people think in something different to do, something to give meaning to their lives. Not just to work and go to the supermarket and the shopping center and, pum, buy buy buy. Then some of them meet in "strange" associations. Some of them need to follow a leader (I can't stand it, but it's the truth).
In some way, all sects are religious. They're based on faith, with or without a god (but god can be a politician or a football soccer player). They're not necessarily offensive, sometimes they're just like a child game.
Anyway, the subject of sects is not that simple. Sects have been there since the beginning of the times. Sects don't follow the rules of an "official" or institutional organization. That makes them, sometimes, more interesting. Sects must have a limited number of persons; just like some local fans club. Anyway, it tells us about that something's not working in our society (what a discovery!). Ergo, it's not that sects are a threat to society, it's that society has intrinsic threats to its members.
Unfortunately -I think- most people who joined a sect has nothing new to say. They just need something to cling to.
By the way, Szandor LaVey rules!
And no, I don't know anyone who joined a sect so far.