You have raised a very important question; it is something we need to address seriously, for it has been a source of much confusion not only among non-Muslims but also among Muslims in many quarters.
Like any Islamic issue, in order to find a satisfactory answer, we must study in a way that harmonizes the scripture and reason. This is the correct Qur’anic perspective that all believers must adopt in approaching any issue of religion. One of the most fundamental principles of the Qur’anic world view is that we must never allow ourselves to surrender our rationality and common sense in holding on to antiquated beliefs and practices, as was the case with the pagans in the pre-Islamic times. So let us reason about this in a manner that does justice to the sound teachings of Islam and our own sense of rationality and common sense.
Let us assume for a moment that most Muslims today (mind you there are over 1.5 billion Muslims out there) are simply holding on to their faith and failing to renounce it for fear of the death penalty. It looks absurd for anyone to hold such a view; it begs an answer for the following reasons:
1. Why did people embrace Islam in the early days when the faithful were subjected to all sorts of trials, tribulations, and persecutions? They were even forced to flee their homes and possessions in order to secure freedom of conscience to practice their religion of choice.
2. How do we explain the historical fact that in virtually all of the conquered territories such as Iraq, Syria, Iran, and Egypt, an enormous number of people entered Islam quite willingly even though they were allowed to remain as they were: Christians, Jews, Zoroastrians, and so on?
3. The Spanish Inquisition instituted against the Muslims and the Jews is a historical fact. Why did many preferred to opt for expulsion or death instead of conversion to Christianity?
4. As the European historians have recorded, thousands and thousands of both Muslims and Jews were slaughtered by the Crusaders in the holy lands; the blood of the victims ran knee deep in the streets of the holy land. Why didn’t they choose to embrace Christianity in order to escape their miserable fate?
5. There are today over 1. 5 billion Muslims in the world coming as they are from diverse racial, ethnic, and religious backgrounds. We ought to ask ourselves: Why did such a huge mass of humanity embrace a faith which allegedly teaches such crude notions? Why did they forgo their allegedly superior beliefs and practices?
6. How do we explain the fact that Islam is still the fastest growing religion in the world in spite of the horrendously negative image of Islam and Muslims that is often projected?
7. Newspapers in Great Britain report that an increasingly large number of men and women are converting to Islam in Great Britain in spite of the extremely negative publicity against Islam. The irony is that the majority of those who embrace Islam are women, despite the fact that the media project them as the most disadvantaged in Islam. Whose sword is driving them to join the fold of Islam?
8. Finally, those who allege that Islam was spread through the sword may do well to read an excellent study on the spread of Islam by a former Christian missionary to India and a late professor of Islamic studies at Aligar Muslim University, namely Thomas Arnold; his work is entitled The Preaching of Islam.
Now coming to the false notion that everyone who leaves Islam is automatically killed, I can assure you that this was certainly not the case in many cases. Even though the penalty for treason was the death penalty (as was the case in the Law of Moses as well), there was no targeting of people who simply chose to leave Islam without any implication of treason. To simply kill anyone who chooses to follow a religion other than Islam is against the fundamental teachings of the Qur’an. Freedom of conscience is a fundamental principle of the Qur’an that is clearly stated in many Qur'anic verses. I list just a few:
[Had your Lord willed, all the people on earth would have believed. So can you (Prophet) compel people to believe?] (Yunus 10: 99).
[Say, ‘Now the truth has come from your Lord: Let those who wish to believe in it do so, and let those who wish to reject it do so’] (Al-Kahf 17: 29).
[So (people) respond to your Lord before there comes a Day that cannot, against God’s will, be averted—you will have no refuge on that Day, and no possibility of denying (your sins). If they still turn away (remember that) We have not sent you (Prophet) to be their keeper: your duty is to deliver the message] (Ash-Shura 42: 47-48).
[There is no compulsion in religion: true guidance has become distinct from error, so whoever rejects false gods and believes in Allah has grasped the firmest hand-hold, one that will never break. Allah is all hearing and all knowing] (Al-Baqrah 2: 256).
