The text states that "The line between crowd control and thought control can be very thin." How that is so?

Answer 1

well, if you were to force people who want to protest to be confined to certain areas, that could be thought control. You claim to be controlling the crowd, but you are also keeping them from voicing their opinions.

Check out this "Free Speech Zone". It looks more like a "lock these hippies up Zone"

http://en.wikipedia.org/wiki/Image:First_amendment_zone1.jpg