Allah, or God in English, created human beings to worship Him alone and instilled within them an inclination towards doing that.
"And I did not create Jinn and men, except that they should worship Me alone." (51:56)
"And remain steadfast on the pure religion, the faith with which Allah created mankind. There is no alteration in the religion of Allah." (30:30)
Prophet Muhammad said, "Every infant is born with an innate disposition (towards knowing and worshiping their Creator alone), but it is his parents who make him a Jew, or a Christian or a Magian." (Reported by Bukhari and Muslim)
So even though everyone is designed and programmed to be Muslims, they may not be raised as such, depending upon outside influences. This is different from apostasy.
An apostate is someone who leaves the religion of Islam for another religion. One is considered an apostate if he does this while being sane, and of his own free-will, without being forced.
The punishment for apostasy is similar to treason in most countries. The ruling of the apostate is that he is given an opportunity for three days to repent and return to Islam and he is encouraged intensely to do so. This is done by trying to dispel any doubts or misconceptions that he may have about Islam, making sure that he understands his decision. If he returns to Islam, he will be left alone, and if not, he is killed with the sword.
Prophet Muhammad said, "Whoever changes his religion (away from Islam), then kill him." (Reported by Bukhari)
If the apostate is killed, he is not washed (in Islamic ritual manner), prayed over (the Islamic funeral prayer) or buried in the cemeteries of the Muslims. He is not inherited from and whatever he left of wealth belongs to the Islamic State and should be used for the general benefit of the Muslims.
The purpose of performing capital punishment upon the apostate is to deter the remainder of society from repeating such an action. And of course this is to be done in a land in which Islamic Sharee'ah is established.
It is well known that in Madinah there existed a number of Jewish tribes and that some of the first protectors of the Muslims were the Abyssinians, who were Christians. Muslims also preserved the places of worship and the lives of the Christians and Jews in Muslim controlled Palestine and Spain. Had it been that every non-Muslim was considered an apostate, these events would never have happened.