This is what really confuses me about the whole thing. While I wouldn't agree with it, I could at least somewhat understand if they were actually defending Muslims from outside attacks. But as you say, they're not. They're going to fight against Muslims.
Exactly, which is why I think of those fighting in ISIS as idiots and hypocrites. Even when we are talking about the Assad Regime, there are Muslims on that side.
This is how they justify themselves:
In Afghanistan, it was a communist government led by a Muslim I think that implemented policies that involved killing off a lot of prisoners, who were mostly religious leaders. Remember, this was a government controlled by Muslims.
The Iran-Iraq war was fought by governments also controlled by Muslims, and the war was kind of initiated by the US.
The Syrian revolution was the same problem. Government controlled by Muslims using violence to eliminate the voice of other Muslims.
So how do we know who is a true Muslim, and who is merely a puppet for someone else?
Their assumption is that if any Muslim is even affiliated with another type of government, then that means they have given up their allegiance to Islam, and not a Muslim.
Basically, what that means is that if they're not fighting with us, they're fighting against us. They assume that Shi'a Muslims or the Muslims part of the Syrian government are hypocrites, which would justify their death.
That is my guess. But yeah, nothing can ever go right when a Muslim fights another Muslim.
As the Messenger said, "Once the sword has been sheathed against a Muslim, it will not be unsheathed until the day of judgement." The first occurrence was in 661 A.D. Go figure.