Disputation is the Gate of Heresy

“The Messenger of Allah (sal Allahu alaihi wa sallam) said: ‘A people have never gone astray except that they were given to disputation.’ He (sal Allahu alaihi wa sallam) then recited: ‘They mention this to you, only by way of disputation. No! But they are a quarrelsome people.’ (Quran: Surah Zukhruf, Ayat 58)” [Ahmad]

If you wish to be firm upon the truth and the way of Ahl us-Sunnah before you, beware of Kalaam (the discipline of seeking theological knowledge through debate and argument) and the people of Kalaam, and of disputation, arguing, analogy and debating about the Religion. Listening to them, even if you do not accept from them, throws doubt into the heart. This is sufficient for you to be destroyed. There has never been any heresy, innovation, innovated sect or misguidance except through theological rhetoric (Kalaam), disputation, argumentation and analogy. These are the gates of innovation, doubt and heresy. [“Explanation of the Creed” by Imam Al-Barbahaaree]

While this point contains a prohibition of disputation, it does not forbid what is necessary as regards rebutting and replying to the doubts and false beliefs spread by the innovators.

The average person should do his best to shield himself from those who corrupt beliefs. Instead of trying to guide the misguided yourself, refer them to the learned in religion. 

If someone has AIDS and you are not a doctor you will not begin treating them and operating on them no matter how much of a well wisher you are. It would be cruel to the patient and asking for trouble for yourself if you were to attempt their cure. Similarly, do not debate with the misguided nor allow them to influence you.