What do you think his Purpose for the Black Lanterns are?

To kill everything. Seems obvious.

Not really,I thought that too, but there has to be something more to it. I don't think they would have built the Black Lanterns up as much just to lead us to a typical kill everyone scheme.

Well Nekron is the embodiment of death, and throughout the series there is mention of how the living disturb his sleep. If there is an ulterior motive to the one we know, Geoff Johns is keeping a pretty tight lid on it.

That's true.

that collar was lame..

I find Sinestro a far more interesting character
 
too bad Geoff always makes him jobber  
all this hype about the writing and Johns blows it then artists save Johns ass with some silly splash pages
 

 
Maybe a new writer can step in during brightest day and give us some better answers

in a way nekron is something of an anti hero, he sees that the original guardians failed their task in bringing peace to the galaxy

he came to the conclusion that the cause of all turmoil is emotion

therefore he leads the black lanterns to terminate all emotion from the universe and finally bring peace where the green lanterns and the manhunters before them failed

so sort of a noble cause in a twisted extreme way,

it would ultimately result in peace but at the price of killing anyone who shows emotion of any kind