All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is not permissible to teach the books on other religions like Judaism and Christianity or any other false religions to the young Muslims as an academic subject because a misconception may affect the heart of one of these young Muslims and he will not be able to get rid of it, and so, it will be a reason for his affliction in his religion [i.e. it may turn him away from Islam]. So this is a matter that we should be aware of.
However, if there is a group of students who are well-versed in Islamic religion knowledge, and the Muslim community wanted them to specialize in studying these religions in order to know their falsehood, so that they would be able to refute the misconceptions of the people of falsehood, then in such a case, this is permissible. Rather, this is a kind of communal obligation.
For more benefit, please refer to Fataawa 8036 and 27803.
Allaah Knows best.