Last week, the Rebbe mentioned the idea that, for a certain person, the Torah will only make his bad middos and taavos worse. (See here about the zav and zavah.)
It seemed to me that in the Yeshiva world, the general consensus is to just learn Torah anyways, even if the person is "tamei", as the Torah has a cleansing quality which over time will right whatever malevolent roots are in the person. Torah can and should be learned by anyone to purify the mind and steer the heart back to Hashem.
In Chassidus, while that idea is definitely spoken about, it seems that there is a much greater emphasis on the preparation that must take place in order to be worthy, so to speak, of learning Torah. As the Rebbe quoted Chazal (Yoma 72b), "If the person merits, the Torah becomes for him like an elixir of life. If he does not merit, the Torah is like a fatal poison."