Ruling on studying western theories that go against sharee’ah

Shaykh Muhammad ibn Saalih al-Uthaymeen
(may Allaah have mercy on him) was asked this question, and replied
as follows: 

I say that this is undoubtedly jihad
for the sake of Allaah, for a person to study these theories that go
against Islam in order to refute them from a standpoint of knowledge. 

Hence the Prophet

(peace and blessings of Allaah be upon him) said to Mu’aadh, when he
sent him to Yemen, “I am sending you to some people from among the People
of the Book.” (Narrated by al-Bukhaari, Kitaab al-Zakaah, 1395;
Muslim, Kitaab al-Eemaan, 29). He told him about them so that
he would be prepared to deal with them. Similarly, the scholars who
studied these matters, such as Shaykh al-Islam Ibn Taymiyah, who studied
various branches of knowledge and philosophical issues and the like
so that he could refute their proponents. 

If you are studying these matters in
order to refute them, and you are confident that you are able to refute
them without being affected by them, because you worship Allaah much
and fear Him, then I hope in sha Allaah that this will be good for you
and of benefit to the Muslims. But if you cannot refute them in a rational
manner or with proof, do not follow this route. Similarly if you are
not completely certain and deeply convinced, then I advise you to leave
these matters alone, for they are dangerous. No one should expose himself
to problems when there is the fear that he is not able to tackle them
properly.