Pay closer attention to what is happening and/or the conversations taking place when it shows up.It's not about being religous.I'm trying to remember this correctly. It didn't pass judgment on Mr. Eko then kill him, did it? Didn't it say that if Mr. Eko asked for forgiveness then he could live, but Eko said "no, I nothing to be sorry about. I did what I did to survive." It was then that smokey killed him. Not because he was guilty, but rather because he wouldn't ask for forgiveness.
Which is really interesting because we haven't seen smokey ever give anyone else that choice to make. Was it because Eko was a religious man and the others smokey killed were not? Does Smokey kill you based on your faith (or lack of it)? If your catholic do you get a chance to attone for your sins like you do in confession? So, if smokey had shown up to kill Charlie (who was also catholic) would Charlie have been given the chance to ask for forgiveness? If you have no religious beliefs does it kill you without thought? What happens if you are Jewish or a Hindu? Is Smokey some sort of guide to the afterlife (The Egyptians believed in something like that didn't they?) and as a "guide" to the afterlife does it judge you based on how you judge yourself?
Echo was religious but was also a man that used violence as a solution, which is hypocritical of what religion is meant to teach. Due to Echo not seeing the wrong in violence, Smokey passed judgement on him and killed him. The Island thru the "spirits" certain people meet are testing them. It asks them clever questions that reveals themselves.
Remember when Ben summoned it? Ben said he didn't control it, yet it only went after the military men. The men holding guns.
Rousseau called it a security system for the island. So it stands to reason it kills those on the island that it views as threatening.
But what about the pilot? He never was visited, just outright killed and then smokey chased Jack, Kate & Charlie. If it wasn't going to kill them then why chase them? Why did it try and take Locke? Why did it take one of Russo's crew, but not the others? Why did it try and get Kate and Juliet? And since it did try and get them, why hasn't it tried to get them again? Why did it let the Widmore's Mercs live and not kill them like it has done to everyone else it has attacked?
There has got to be a lot more going on that we don't know (obviously) but so far the only times we have seen it give someone a chance to go free was when it gave Eko a chance to ask for forgiveness for what he had done and he said no, so it killed him. And another time when it rose up above Locke but didn't kill him (we still don't know what Locke saw (except it was beautiful)) and we don't know if it talked to him or not at that time.
We are also assuming that Smokey and the "ghosts" are one and the same, when really it could be two different beings. It could be that smokey roams the island killing whoever it wants and then when the "Ghosts" call it it shows up and kills whoever the "ghosts" tell it to before goingback to doing its own thing.
As I said, Russo called it a security system for the island.
It wanted Locke but Locke wants to be taken by it because he doesn't fear it.
It chased Juliet & Kate but didn't kill them. They hide in a tree and you saw flashes from it. If it's smoke that uproots trees, how is the tree Juliet & Kate hiding in keeping it out unless it doesn't wish them harm.
It took the first member of Russo's crew that armed himself.
It did kill Widmore's Mercs.
If you watch more closely, there is a pattern forming of what this thing does.