How do you forbid to think? One's thinking energy is not anyone's to set rules on nor to own. To forbid to think, or, to force one to think in a certain pattern is, primarily, changing the nature of the whole process; it becomes intellectual enslaving; mental rape. Believing so results from the lack of self-awareness, and the disregard to one's status as a limited creature that has no control on the intellectual property of another creature; one is free to think, freely, according to what one chooses to be right and sane.
One may have the power to stop somebody from saying what they think, but they sure know, that they lack the slightest power to forbid them to think; they're still limited creatures, and they always will be.