I wrote a tract about this on my blog and Id like to reproduce it here. It did have a couple of extra points on it, but I have removed those because they dont apply
until some muslim brings up a rather silly analogy. At any rate:
A Treatise Against the Punishment and Execution of Apostates
1. A person forms a belief when (s)he reaches a conclusion after a specific observation of events, ideas in action, natural phenomena, and suchlike. This person does not form this belief purely out of spite, vindictiveness or immorality, but by sincere contention. I therefore consider it unreasonable, unrealistic and utterly fascistic and totalitarian to punish someone for a conclusion they cannot help but reach.
2. Deciding that Islâm carries as much truth as any other manmade religion, and thereby labelling it false after believing it as true, represents nothing more than a change of belief.
3. Agreeing with the concept of execution for apostates means advocating (statesanctioned) murder of people who reject what they now believe as nothing more than legends, fairytales and ancient fables.
4. Receiving punishment for changing your belief means that an exmuslim ends up compelled by force to remain at least for show in that specific belief. This I would describe as nothing other than compulsion, and renders the famous ayat at 2:256 in the Qurân patently false.
5. Death for apostates merely extends the charade of Islâm utter hypocrisy, and the Qurân itself denounces hypocrisy. Killing in the name of hypocrisy simply turns fundamentalism into another idol, and sacrificing apostates to this idol represents shirk worshipping others as God, and effectively dismantling the tawhîd of Allâh.
6. Punishing someone with execution for apostasy from Islâm (or any other cult) remains, in my opinion, a fundamentally despicable concept. It displays a complete and shocking lack of empathy and understanding as to what motivates someones convictions (in other words, something they cannot help but believe, and not necessarily a free choice).
7. This makes it a complete attack on freedom of thought, on freedom of speech and as such we, as rational and straightthinking people, must speak out and act against it wherever we encounter it. It deserves nothing else but utter contempt and scorn.
8. Brutally murdering a murtad does not prevent harm in the slightest. The affected victims family and friends, his/her workplace, and so on, all lose someone dear or essential to them simply because that person had the audacity to believe something and change their mind.
9. Additionally, how does this affect a persons position in the (I believe nonexistent) Afterlife? Executing the apostate will not absolve him/her of supposed sinfulness, which means (s)he will not go to heaven. Threatening someone with death does not cause them suddenly to change their deepseated philosophical views. Any claim to the contrary by the apostate in question amounts to blatant insincerity and, therefore, we can discard the sentiment as meaningless.