The Thought Police are those people who would like to control other people's lives to the extent that the expression of certain thoughts is banned. They would prefer to be able to control the actual thoughts themselves, but not yet being gods, they grudgingly accept that it is still only the expression that they can't do anything about. The right-wing equivalent of the politically correct movement, the Thought Police operate in many different realms, but their average concentration rises sharply in the ranks of the religious fundamentalists.
The phrase Thought Police may provoke imagery of extreme examples, but anyone can be guilty of acting judgmental of other people's thoughts.
The witch hunt for pedophiles has perverted social expectations. While child molestation is often punished more severely and with less due process than murder, someone thinking of molesting children stirs greater outrage than someone who likes to think of murdering people (such as the pretend-play in many popular video games today). For example, Jack McClellan's only (proven) crime is to admit his thoughts of molesting children and being naive enough to share his thoughts publicly. Since then he has had numerous death threats and at least one restraining order for his thought crime.