Because it really is easier to mislead people as a group, dear JeffT (peace to you!)... than individually. While often touted in the western world (but not really, and almost utterly rejected in the eastern world)... individuality is more dangerous than groupthink. That's why they DF for individual thinking - it can become a "cancer" that ultimately affects the groupthink. Makes it more difficult to mislead the group. Where groupthink exists, however, control of the entire unit is much easier. It's like the Star Trek Borg - you need the entire group in order to successfully carry out your agenda and so non-assimilation is unacceptable. And assimilation... must be absolute.
The world was kind of heading in that direction, more individuality, around the turn of the 20th century. Then came things like communism... and, after that, the progression of the Watchtower Bible & Tract Society. Two steps forward... six steps back!
I hope this helps and, again, peace to you!
A slave of Christ,
SA