But you do not have to go into their minds at all, merely the space their minds inhabit. In fact, all of a person's knowledge, when they are thinking of it, is emitted by them, much like a radio signal broadcast in the clear. Some are loud, some are not, but if you spent even a few days wandering the lecture halls, study halls and offices of the psych area, you'd never have to invade a single mind. Just soak it in.
If you are speaking of delving into man actual mind and stealing personal information, then yes, it would be unethical. But the knowledge that they are emitting? No.