Here's a short piece on the issue of Freedom of Conscience in Islam - explaining what Islam teaches and referring to what God instructs in the Quran on the subject. Based on these verses, we can see that the belief among many Muslims that apostacy is a crime that is punishable by man has no basis in the Quran or Islam (i.e. it is a man-made innovation, not supported by the Quran).
Freedom of Conscience
Islam has proclaimed complete freedom of conscience. The Qur'an is unique among all the scriptures in affirming truth and righteousness of all the Prophets and the truth of all Divine revelations, and in establish and proclaiming the right of every human being to complete freedom of conscience:
There should be no compulsion in religion. Surely, right has become distinct from wrong.. (Ch.2: V.256)
Again,
And say, 'It is the truth from your Lord; wherefore, let him who will, believe, and him who will, disbelieve.' (Ch. 18: V.29)
The presentation of Islam to mankind must involve no pressure or coercion. Indeed no pressure or coercion was possible, as the Holy Prophet (sa) stood alone and unprotected against a hostile combination of tribes and he and his handful of early followers were subjected to the most bitter, cruel and persistent persecution all through the thirteen years of his ministry at Mecca. The manner propagation of the, faith is, however, laid down clearly the Qur' an:
Call unto the way of thy Lord with wisdom and goodly exhortation, and argue with them in a way that is best. Surely, thy Lord knows best who has strayed from His way; and He knows those who are rightly guided. (Ch. 16: V 125)
A way of accord between all those who believe God and in Divine revelation has been proclaimed in the Qur'an. The time seems to have come, it cannot be far when the invitation extended by Islam may be availed by the followers of other revealed faiths, for the purpose of achieving a practical brotherhood of man through common spiritual values.
Say, `O people of the Book! come to a word equal between us and you that we worship none but Allah, and that we associate no partner with Him, and that some us take not others. for Lords beside Allah.' But if they turn away, then say, `Bear witness that we have submitted to God' (Ch.3: V64)
As a corollary of belief in the existence and unity of God and in a divine purpose behind all creation, Islam emphasises the accountability of man in all spheres of life, and sets up a balance between this life and the hereafter. This constitutes the essence of Islam. Whoso, therefore, affirms faith in the existence and unity of God in the life hereafter and strives constantly after righteous action, becomes heir to the grace and mercy of God:
Surely, those who have believed, and the Jews and the Sabians and the Christians-whoso believes in Allah and the Last Day and does good deeds, on them shall come no fear, nor shall they grieve. (Ch.5: V69)
It will thus be seen that Islam does truly speak to man at a universal level and seeks, through the acceptance of common values which are essential to the preservation and fostering of man's moral and spiritual life to bring about accord in the religious sphere.