Concerning Horcuxes

[Anna]

No: HPFGUIDX 169378

Rereading HBP, just past the part when Dumbledore shows Harry the TRUE 
memory of Slughorn, young Voldemort, and their conversation about 
Horcruxes, I still don't understand something:

Slughorn says that killing someone splits your soul, and that with 
said piece of soul, you can create a Horcrux.  Well, what about all 
the Aurors and others who killed in the numerous battles 
between "good" and the forces of Voldemort.  If they (the Aurors) 
killed dark wizards and such when trying to capture them, for example, 
aren't their souls split as well?  I mean, does the mere act of 
killing someone -- anyone -- split the soul, or is the soul only split 
when one does a particulary nasty/evil murder, or has the concious 
intention of creating a Horcrux?  Voldemort did countless murders, yet 
he only supposedly created 6 Horcruxes.  Do you think his soul is 
really split into a hundred-some-odd pieces?  Any ideas?  Thanks.

Anna