Whereas, a muslim who follows the First Half, but does not practice the Second is an apostate and so must be killed by any muslim practicing the 2nd Half.
To further complicate matters, a muslim from one sect is often bound to kill another from a different sect. Worse still, a muslim from one sect who follows on cleric/imam can be bound to kill another from the same sect for following a different cleric/iman. An illustration follows:
A Comparative Tale of Two Religions
Christian vs. Christian
A man was despondent. His life seemed worthless. He decided to end it all and climbed up onto a bridge railing high above a raging river.
Just as he was leaning forward to make his final plunge, a man happened by and said, “Wait. Let me help you.”
“How can you help me? My life is over?”
“Are you a Christian, Jew, Hindu or Muslim?”
“A Christian”
“So am I! What denomination are you?”
“I used to be a Catholic, but have not been to mass in decades.”
“I’m a Protestant. Let me help you find your way back to life.”
“What can you possibly tell me?”
“I can tell you that Jesus loves you and for His sake and His love of you, you cannot take your life. There is so much more to live for.”
“Like what?”
“Children.”
“I don’t have any.”
“Neither do I. But there are still children in need of adults to guide them. Would you deny some child your wisdom and experience?”
“No, of course not!”
“Then step back and come with me.”
So the two men walked off.
Muslims vs. Muslim
Far away in a distant land, another man stood on a different bridge.
A man was walking across a bridge one day, and he saw a man standing on the edge, about to jump off and commit suicide.
He immediately ran over and said, “Stop! Don’t do it!”
“Why shouldn’t I?” the other replied.
The man said, “Well, there’s so much to live for!”
“Like what?”
“Well… are you religious or atheist?”
“Religious.”
“Me too! Are you Muslim, Christian or Jewish?”
“Muslim.”
“Me too! Sunni or Shi’ite?”
“Sunni.”
“Me too! Hanafi, Hanbali, Shafi or Maliki?”
“Hanafi.”
“Wow! Me too! Do you follow Sheikh Fulaan al-Fullani or Sheikh Kaza Kazah?”
“Sheikh Fulaan al-Fullani.”
To which the first man said, “What?!! Die, heretic scum!” and pushed him off.
From: Spengler’s The Devil’s Sourdough and The Decline of Nations