I have attended many seminars regarding the Islam to know it closely so that my some of the assumptions be cleared as much as possible. One of the e-seminar that I just watched was of Dr.Zakir. He wanted people to believe in Islam, and to get converted in to their community. Why would and person want that to be done?
My answer will not explain the actions of Dr Zakir, however, I will touch on the topic.
In Islam, it is our duties to convey and make others aware of the teachings of Islam as this is what we were commanded to do.
“Convey (my teachings) to the people even if it were a single sentence” (Sahih Bukhari, Vol.4, Hadith 667)
Who is better in speech than one who calls to Allah, does righteous deeds and says indeed I am among the Muslims. Quran, Sura 41 (Fussilat), ayah 33
“Therefore do thou give admonition, for thou art one to admonish. Thou art not one to manage (men's) affairs.” (Quran 88:21-22)
As most Muslims are firmly bonded with their religion, they follow the teachings of Islam, as mentioned within the Hadeeth below, that we should love to our brothers in religion and humanity what we love to ourselves, therefore as we love our religion we wish that our brothers in humanity and faith love it too! which may be another reason why we invite others!
On the authority of Abu Hamzah Anas bin Malik (may Allah be pleased with him) - the servant of the Messenger of Allah (peace and blessings of Allah be upon him) - that the Prophet (peace and blessings of Allah be upon him) said : "None of you will believe until you love for your brother what you love for yourself." Related by Bukhari & Muslim
Although that we invite or give others information about our religion, this does not mean that we have to force or compel people to join or act upon the teachings of the religion, as the most important aspect is faith and only God knows whether a person has it or not!
“Let there be no compulsion in religion: Truth stands out clear from Error:” (Quran 2:256)
In regards to your comment, all Muslims are aware of the presence of other religions, we simply don't agree with the teachings and that's it, we don't have to do anything else!
“To you is your religion, to me is mine” Quran 190