Apostasy in Islam is punishable by death. This sentence is practiced wherever Muslims are in power and can practice it. In Iran many Baha'is where executed because they changed religion. The Fatwas against Salman Rushdie, Taslima Nasrin and Anwar Sheikh are examples of that.

Muslims are trained to have fanatical devotion. They won't hesitate to do any crime if it is done in the name of Allah. Islam is a moral relativistic religion. It means that stealing, lying, terrorism and even assassinations are acceptable if are done for Allah and his cause.   

"Make no excuse; you have disbelieved after you had believed. If We pardon some of you, We will punish others amongst you because they were criminals" [Quran 9:66]

"Verily, those who disbelieved after their Belief and then went on increasing in their disbelief - never will their repentance be accepted [because they repent only by their tongues and not from their hearts]. And they are those who are astray. Verily, those who disbelieved, and died while they were disbelievers, the (whole) earth full of gold will not be accepted from anyone of them even if they offered it as a ransom. For them is a painful torment and they will have no helpers."
[Quran 3:90-91]

"O you who believe! Whoever from among you turns backx from his religion, Allah will bring a people whom He will love and they will love Him; humble towards the believers, stern towards the disbelievers, fighting in the Way of Allah, and never afraid of the blame of the blamers. That is the Grace of Allah which He bestows on whom He wills. And Allah is All-Sufficient for His creatures' needs, All-Knower." [Quran 5:54]

"O Prophet (Muhammad)! Strive hard against the disbelievers and the hypocrites, and be harsh against them, their abode is Hell, - and worst indeed is that destination. They swear by Allah that they said nothing (bad), but really they said the word of disbelief, and they disbelieved after accepting Islam, and they resolved that which they were unable to carry out, and they could not find any cause to do so except that Allah and His Messenger had enriched them of His Bounty. If then they repent, it will be better for them, but if they turn away, Allah will punish them with a painful torment in this worldly life and in the Hereafter. And there is none for them on earth as a Wali (supporter, protector) or a helper." [Quran 9:73-74]

"So remind them (Muhamad), you are only one who reminds. You are not a dictator over them. Save the one who turns away and disbelieves. Then Allah will punish him with the greatest punishment. [Quran 88:21-24]

It seems that the above verse contradicts itself. On one hand the choice of faith is left to the individual and God tells Muhammad that is is not to force faith on them and immediately he makes an exception with those who choose to reject Islam after accepting it. This is an flagrant proof of the cultic nature of Islam.

The following verse is about the Meccans who after accepting Islam did not want to emigrate at Muhammad's behest or wanted to go back to Mecca, to their homes and lives. Muhammad orders his followers to kill those who defect the camp. This is a very harsh sentence against the Muslims who were fed up and just wanted to go home. 

"They long that ye should disbelieve even as they disbelieve, that ye may be upon a level (with them). So choose not friends from them till they forsake their homes in the way of Allah; if they turn back (to enmity) then take them and kill them wherever ye find them, and choose no friend nor helper from among them," [Quran 4:89]

"They swear by Allah that they said nothing (evil), but indeed they uttered blasphemy, and they did it after accepting Islam; and they meditated a plot which they were unable to carry out: this revenge of theirs was (their) only return for the bounty with which Allah and His Messenger had enriched them! If they repent, it will be best for them; but if they turn back (to their evil ways), Allah will punish them with a grievous penalty in this life and in the Hereafter: They shall have none on earth to protect or help them." (Q.9:74)

There are also many hadithes that confirm what is in the Quran about the harsh treatment of the apostates. Here are a couple of them.

 (Sahih Bukhari 4.260) 

Narrated Ikrima:
"Ali burnt some people [hypocrites] and this news reached Ibn 'Abbas, who said, "Had I been in his place I would not have burnt them, as the Prophet said, 'Don't punish (anybody) with Allah's Punishment.' No doubt, I would have killed them, for the Prophet said, 'If somebody (a Muslim) discards his religion, kill him.'" 

Sahih Bukhari 9.58 (also Sahih Bukhari 9.271):

Narrated Abu Burda:
".... The Prophet then sent Mu'adh bin Jabal after him and when Mu'adh reached him, he spread out a cushion for him and requested him to get down (and sit on the cushion). Behold: There was a fettered man beside Abu Muisa. Mu'adh asked, "Who is this (man)?" Abu Muisa said, "He was a Jew and became a Muslim and then reverted back to Judaism." Then Abu Muisa requested Mu'adh to sit down but Mu'adh said, "I will not sit down till he has been killed. This is the judgment of Allah and His Apostle (for such cases) and repeated it thrice. Then Abu Musa ordered that the man be killed, and he was killed. Abu Musa added, "Then we discussed the night prayers and one of us said, 'I pray and sleep, and I hope that Allah will reward me for my sleep as well as for my prayers.'"