Why does nobody just kill a main character when they have them captured?

[False Dragon1991]

It happens A LOT in this series. Especially to the supergirls who are beyond useless at this. Despite us knowing that the servants of shadow are supposedly ruthless killers without scruple none of them will ever just slit the throat of any of our main character. Why take the risk and time of corrupting them? Plus in later books where the likes of Elayne are clearly enemies of the shadow they still refuse to just kill Elayne when they have her at her mercy. To me, especially given the sheer number of instances where this happens, it is really silly and unrealistic. If your opponents are supposed to be ruthless and void of humanity then they should have no qualms in murdering unarmed prisoners. Yet the supergirls repeatedly walk away from captivity without injury or anything missing? What happened to being caught by the shadow being a fate worse than death itself? 

[Agitel]

It should be apparent by now why Rand was kept alive. But as to your last question...

 

 

 

Keep reading.

[Rhienne]

I think at one point Moghedian comments that Nynaeve's great strength means it would be a waste to kill her.  Given that the Forsaken have Compulsion and the 13x13 trick, perhaps they think it would be more beneficial to turn them rather than just kill them.

[Barid Bel Medar]

You answered your own question. 

 

 

 What happened to being caught by the shadow being a fate worse than death itself? 

 

A big theme in the series is that death is not the worst thing that can happen to a person. 

 

However, I also suggest you RAFO, as this theme is explored later. 

 

If you don't like that death is not the Shadow's chosen tool, that's fair enough, but then there is really nowhere to go in this discussion. 

 

Edit: To be fair, they do have their share of fortuitous escapes where Darkfriends were trying to kill them, but the majority of the Shadow's top agents want the main cast captured, not dead. 

 

Except Perrin and Mat. 

 

Mat has the most dangerous assassin created chasing him, and Perrin has the most dangerous human assassin after him.