Conditions of engaging in dialogue with Christians
14-2-2012 | IslamWeb
Question:
There is a channel on Paltalk that includes some Christians. I was surprised that they blaspheme the Prophet, sallallaahu ‘alayhi wa sallam, and I could not do anything because they are many people in the face of one or two Muslims.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
The enemies of Allaah The Almighty cannot do anything that harms Islam but such kind of blasphemy and insulting. However, the Muslim should shun such ignorant people in order not to expose Islam to their abuse.
Allaah The Almighty Says (what means): {And do not insult those they invoke other than Allaah, lest they insult Allaah in enmity without knowledge.} [Quran 6:108]
It is impermissible for you to visit such websites or to engage in dialogue with people there if you feel that you are unable to refute their claims and prove the veracity of Islam. Allaah The Almighty Says (what means): {And it has already come down to you in the Book that when you hear the Verses of Allaah [recited], they are denied [by them] and ridiculed; so do not sit with them until they enter into another conversation. Indeed, you would then be like them.} [Quran 4:140]
If you visit such websites and enter into a debate in which you cannot provide your argument and defend Islam; then, you harm yourself and your religion.
The Prophet, sallallaahu ‘alayhi wa sallam, said: “‘The believer should not humiliate himself.’ They (the Companions) asked, ‘How can the believer humiliate himself?’ The Prophet, sallallaahu ‘alayhi wa sallam, replied: ‘By overburdening himself.’” [At-Tirmithi]
Perhaps you do not know that the arguments of the Christians are very weak. Shaykh Ahmad Deedaat 
debated many famous priests and Christian scholars and silenced them with arguments in front of the people. These debates were published.
If you have the ability to argue in a good way; then, you have to support yourself with knowledge especially knowledge of the Sharee‘ah (Islamic law) and comparative religion. Otherwise, it is impermissible for you to get involved in this field.
Allaah Knows best.