What is the ruling on a university student studying Western theories that contradict the teachings of Islamic law, with the intention of critiquing them and benefiting the Islamic nation through his current studies and after graduation?

If you study theories that contradict Islam in order to refute them with knowledge, and you possess devotion, piety, and confidence in your ability to refute them without being influenced by them, then this is good and beneficial for Muslims and is considered a form of striving in the way of Allah. This is similar to what the Prophet, peace and blessings be upon him, did with Mu'adh ibn Jabal, and what Shaykh al-Islam Ibn Taymiyyah did. However, if you do not have evidence or are not firm and steadfast, then you should not embark on this dangerous path.