I like your thinking and while I believe that something needs to be done about Scientology I'm really not sure what the correct approach should be since as you say any type of government regulation could lead to serious abuse.
I've been very wary of Scientology since I saw the first 60 Minutes piece on it back in the 90's; they seem to have all the earmarks of a cult and seem to practice what could be construed as "mind control"; they discourage their "parishioners" from associating with any non-Scientologist family members and any number of other disturbing practices.
Since I first watched that 60 Minutes piece, I kind of keep an eye out for Scientology news mostly because (believe it or not) I went to high school with Tom Cruise (Glen Ridge High School, Class of 1980) and while I didn't know him or ever remember having met him it still baffles me how someone that I went to high school with could be such a proponent of something that seems so shady. But then on the other hand I'm sure many people went to high school with people that ended up doing really bad things i.e. maybe people who went to high school with Bernie Madoff could say "He was a great guy in high school, I don't know how he went so wrong".