1. Islam is a Deen not a religion, Meaning that, Islam is a comprehensive way of life. Islam is not confined only to some set of ritual actions, no, It penetrates into the heart of economy, society and administrative affairs.
It wants to accomplish Justice, annihilate corruption and inefficiency.
You can read about Economy and Legal Politics in Islam.
2. Apostasy as an act of rebellion is a rare phenomenon.
You must know what is forbidden and what is lawful in Islam!
In Islam it is forbidden to spy on people or your own citizens.
“O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah ; indeed, Allah is Accepting of repentance and Merciful.” [Qur’an, 49:12]
So, basically, someone who wants to distort public/social order plainly is regarded as an apostate, because Islam has greater objectives to preserve.
And, it is no surprise to see such penalty for someone who is plainly rebelling against administrative/constitutional system of a country or structure as an act of treason.
3. This issue has to be discussed from a theological aspect either. This is wrong however to ignore the fact that there are some theological concepts involved in this matter.
Islam wants people to enter paradise, Islam wants to save people from Hell fire, therefore, it views this as a responsibility to keep people from entering Hell fire as much as possible.
This is a Deen [i.e. way of life, religion] ordained by God Almighty for His servants to save them from Hell Fire, God Almighty wants you to abide by His rules and laws.
An Analogy can be as follows,
A mother may punish her child for a good reason to make the child to avoid something bad which may lead to unpleasant future consequences.
4. Apostasy doesn’t always lead to death penalty. A person who plainly targets the administrative and legal system of Islam has to be brought to a legal court and he will be inquired by judge about his/her position, he/she will be questioned about the possible misconceptions or issue that he/she might have about Islam and he/she will be asked to cease quite frequently. After all, it will still be judge’s decision about him/her which is going to be put into effect.
5. Islamic laws [particularly Hudud] can not be implemented [enforced] by individual Muslims. There has to be a legal court. A thing that most people fail to realize when it comes to Islam is that, most phenomena in which people are killed or tortured in Muslim countries are merely done due to some tribal tensions or cultural incentives. I am myself from a Muslim country in an urban area, and I have seen this and heard about it with my own eyes and ears.
6. You can not fully implement Islamic laws unless you have the society and community prepared for it. So, people who fall into illegal actions in Muslim countries are most likely to be excused with a whole lots of reason because person hasn’t the chance to see a real Islamic environment.
We currently have no Islamic state in the world.
7. There is a transparency in Islamic laws and rules. It is quite interesting to notice that Islam has made it quite clear that there is no compulsion in accepting the Deen [i.e. way of life, religion].
“There shall be no compulsion in [acceptance of] the religion. The right course has become clear from the wrong. So whoever disbelieves in Taghut and believes in Allah has grasped the most trustworthy handhold with no break in it. And Allah is Hearing and Knowing.” [Qur’an, 2:256]
And it is quite clear that Islam doesn’t want the person to leave the religion and plainly oppose it after accepting it, this is clear. so, a person has to make up his/her minds truly and sincerely whether she/he wants to become a Muslim or not. Islam doesn’t want to see people playing with Deen [i.e. way of life, religion]! Declaring their faith in the morning and rejecting it in the afternoon [plainly], that was what Jews in early decades of Islam were trying to do,
” And a faction of the People of the Scripture say [to each other], “Believe in that which was revealed to the believers at the beginning of the day and reject it at its end that perhaps they will abandon their religion, And do not trust except those who follow your religion.” Say, “Indeed, the [true] guidance is the guidance of Allah. [Do you fear] lest someone be given [knowledge] like you were given or that they would [thereby] argue with you before your Lord?” Say, “Indeed, [all] bounty is in the hand of Allah – He grants it to whom He wills. And Allah is all-Encompassing and Wise.”” [Qur’an, 3:72-73]
8. Islam needs to be studied in its entirety when talking about concepts like apostasy and so on. People can never get to a correct solution if they don’t try to put all the pieces of the puzzle together, and this is true for every ideology.
9. Islam as a comprehensive system has its own rules and regulation compared to other systems in the world, so [if we discuss it from a democratic point of view] as far as the majority are pleased with the laws and regulation laid down by God Almighty, no one can practically say that they are not right.
11. There is a strong philosophy behind Hudud [i.e. barrier, punishment] which serves multiple desirable purposes.