Secular knowledge permitted?

 Maharal(Nesivos HaTorah 1:14):.... However, a practical problem arises in learning secular knowledge. It is prohibited to learn from a teacher who is not fit. However, this is not a valid objection since the prohibition applies only to learning from a heretic in person. It is only close personal contact that is prohibited and thus reading a book composed by a heretic would not present this problem. Nevertheless the question remains whether it is permitted to study their books when they contain attacks against the Torah concerning such thing as the Creation of the world, G d’s knowledge, survival of the soul after death and whether the World to Come exists. Perhaps they should be prohibited because they might be a harmful influence? ... However Avos says that one must know how to respond to heretical views and if one has not been exposed to heresy how would it be possible to respond to these views? Obviously, it is necessary to be aware of the views of heretics. However, this is obviously permitted only if the intent is to learn their views in order to be able to refute them.