Yes, Islam is available for all people. Every child is born with a sound natural disposition, worshiping Allah without a mediator (being a Muslim). So he, without the interference of family, school, or any religious authority, worships Allah directly until the age of puberty, when he becomes competent for religious duties and is held accountable for his deeds. At this time, he either takes Jesus as a mediator between himself and Allah and becomes a Christian, takes Buddha as a mediator and becomes a buddhist, or Krishna and becomes a Hindu, or takes Muhammad as a mediator and, thus, deviates totally from Islam, or remains on the religion of Fitrah (sound natural disposition) worshiping Allah alone. The one who follows the message of Muhammad (may Allah's peace and blessings be upon him) that he conveyed from his Lord is following the right religion that conforms to the sound Fitrah, and anything else is considered deviation even taking Muhammad as a mediator between oneself and Allah.
"Every newborn is born with sound natural disposition, then his parents either turn him into a Jew, a Christian, or a Zoroastrian." [88] Narrated by Muslim.
The right religion that came from the Creator is only one religion. It is built upon belief in the One and Only Creator and worshiping Him alone. Anything else other than this is invented by people. It will be sufficient to visit India, for instance, and say in public: "The Creating God is One", and everybody will reply in unison: "Yes, the Creator is One." This is actually what is written in their books. [89] However, they differ and fight, and may even slaughter one another, because of an essential point, which is: the form and shape in which Allah comes to earth. For example, the Indian Christian says: "Allah is one, but He is embodied in three hypostases (the Father, the Son, and the Holy Spirit)". Moreover, some of the Indian Hindus say: "Allah comes in the form of an animal, a human being, or an idol." In Hinduism: (Chāndogya Upanishad 6:1-2). "He is only one God and there is no second god besides Him." (Vedas Śvetāśvatara Upanishad: 4:19, 4:20, 9:6). "The God, there is no fathers and no master." "It is not possible to see Him, no one can see Him with the eye." "He has no like." (Yajurveda 9:40). "Those who worship the elements of nature (air, water, fire, etc.) delve into darkness. They drown in darkness. Those who worship the Sāmbūti (things that are handmade like the idol, rock, etc)..." (Christianity): (Gospel of Matthew 10:4). "Then Jesus said to him: 'Go away devil, because it is written: You prostrate to your God and you worship Him alone.'" (Book of Exodus 5-3: 20). "You should have no other gods before Me. Do not make a statue or an image of what is in the heaven above, what is in the earth below, and what is in water from underneath the earth. Do not prostrate to them and do not worship them because I am the Lord, your God, a jealous God. I miss the parents' mistakes in the children in the third and fourth generations of those who hate Me."
If people think profoundly, they will discover that all problems and differences between the religious sects and the religions themselves are due to the mediators whom the people take between themselves and their Creator. For example, the Catholic and Protestant sects and other sects, and the Hindu sects, they all differ on the way of communicating with the Creator not on the concept of the Creator's existence. So, if they had all worshiped Allah directly, they would have been united.
During the time of Prophet Ibrāhīm (Abraham) (peace be upon him), for instance, whoever worshiped the Creator alone was adopting the religion of Islam, which is the true religion, yet whoever took a priest or saint as a mediator between himself and the Creator was adopting falsehood. The followers of Abraham (peace be upon him), thus, had to worship Allah alone and to bear witness that there is no god but Allah and that Abraham is the messenger of Allah. Then, Allah sent Mūsa (Moses) (peace be upon him) to affirm Abraham's message. Abraham's followers had to accept the new prophet and to bear witness that Moses as well as Abraham are the messengers of Allah. So, whoever worshipped the calf then, for instance, was adopting falsehood.
When ‘Īsa (Jesus) (peace be upon him) came to affirm Moses' message, the latter's followers had to believe and follow the Messiah and to bear witness that there is no god but Allah and that the Messiah, Moses, and Abraham are the messengers of Allah. So, those who believed in Trinity and worshipped the Messiah and his mother Mary, the woman of truth, were adopting falsehood.
Finally, when Muhammad (may Allah's peace and blessings be upon him) was sent to affirm the message of the previous prophets, the followers of the Messiah and Moses had to accept the new Prophet and bear witness that there is no god but Allah and that Muhammad, the Messiah, Moses, and Abraham are the messengers of Allah. So, whoever worships Muhammad, makes Tawassul (ask Allah by means of intermediary) by him, or seeks aid from him is indeed adopting falsehood.
Islam affirms the basic principles of the divine religions that preceded it and continued till its time and that were brought by the messengers and were appropriate for their time. With the change in need, a new religious phase emerged sharing the same origin but with a different Sharia, adopting graduation in fulfilling the needs, and with the late religion agreeing with the early religions in the origin of Tawhīd (monotheism). By adopting the dialogue method, the believer becomes aware of the fact that the source of the Creator's message is one.
Therefore, the interfaith dialogue must proceed from that essential concept of affirming the one right religion and considering all the rest as false.
Dialogue has existential and faith-related principles and foundations that man is required to respect and proceed from in order to communicate with others. This is because the purpose behind this dialogue is to get rid of fanaticism and personal whims, which are projections of blind fanatical affiliations that stand as an obstacle between man and the truth of the pure Tawhīd, and that lead to conflict and destruction as witnessed in our current reality.