If someone rejects, leaves or criticizes Islam and Muhammad, are they 'innocent'?
You’re asking very good questions - all these questions are questions that Islamic scholars and schools of jurisprudence debate all the time and you should research more in your spare time.
Simply criticizing Islam or the prophet Muhammad pbuh does not give rise to murder - as another poster mentioned, the prophet Muhammad spent his life being derided, attacked and criticized by the Non-Muslim Arab Quraysh tribe.
The Quran teaches that there is no “compulsion in religion” and an individual cannot be forced to become a Muslim with the threat of violence
There is an interpretation of Apostasy (leaving Islam). The Quran itself does not prescribe the death penalty for apostasy/blasphemy except in Sura an Nisa where it states:
“You will find others who desire that they should be safe from you and secure from their own people; as often as they are sent back to the mischief they get thrown into it headlong; therefore if they do not withdraw from you, and (do not) offer you peace and restrain their hands, then seize them and kill them wherever you find them; and against these We have given you a clear authority”
Without context this verse appears to tell us to kill all who leave Islam. However, Allah is speaking to the early Muslims on how to “protect the newly formed Muslim community“.
The Quran was revealed in parts to the prophet Muhammad and therefore the context of when they were revealed to the Muslims is significant.
Apostacy in the early days of Islam (where the Muslims were surrounded by neighboring Arab non-muslim tribes) would have been akin to desertion and treason. It would be like Benedict Arnold defecting to the British.
These individuals who left Islam were likely to betray the early small Muslim tribe in the era of the prophet Muhammad pbuh and, as such was deemed a lawful killing.
Treason laws and life sentences/murder for treason are common place across the world.
Again, the killing for aspotacy/blasphemy is a debate within sharia law - it requires high burden of evidence/proof. It even allows the opportunity for the perpetrator al apologize/repent so they are not killed. This is not an extra-judicial killing.
Within the 21st century, apostasy and treason are generally not the same. Across the Muslim world, individuals who have left Islam are not killed. There are many non-practicing Atheists and non- Muslims in Muslim countries.