If certain Rabbi wishes to enforce his personal belief by printing materials with outright falsehoods, i.e., he lies, In order to scare people into following his views. Is it loshon Hora to publicize this with the factual information even though he may be publicly embarassed?
1. Can you please provide a few examples of the lies which the Rabbi has published. There is some distance between falsely attributing an opinion to a well known authority, falsely interpreting halachic sources, and false threats such as: smoking hashish is physiologically addictive.
A few examples will help clarity the nature of the lies.
2. When you write that he printed his lies, do you mean that he published them in a public way? Or did he disseminate his lies privately?
The nature of the publication is important in this case.
3. The halachot pertaining to embarrassment are not quite the same as those pertaining to leshon ha-ra. Why do you think that publishing the truth will embarrass him?
4. Truth is the seal of Gd and is therefore of vast importance in and of itself. Do you see any additional benefit (to'elet) in publishing the truth, aside from promoting the truth for its own sake?
5. As a matter of practical advice, it is of course advisable to approach the Rabbi in private. Perhaps a private communication can resolve the problem without leshon ha-ra and without embarrassment.
6. It is not clear what your question has to do with medical halacha. Could you explain?