Can there be a net positive role for the presence of evil?
"If you can imagine it then it exists somewhere." - so let's not even go there. Besides, it's hard enough just overcoming entropy.
If you're religious, then yes, there is. Otherwise ItDepends on the evil.
Can there be a net positive role for the presence of black gooey carbon deposits stuck on your barbecue after grilling steaks?
If properly maintained, they prevent rust. :)
The PurposeOfEvil is the same as the PurposeOfParasites?, it is a evolutionary successful strategy. Attaching the attribute "evil" is done by the ones being parasitized. Most of us would prefer not to call our own parasiting actions "evil", though they are of the same kind (e.g. humans are usually parasitizing on everything we eat). -- GunnarZarncke
Hmmm, I am reminded of a passage:
Evil in moderation is what protects us against unlimited evil. -- AnonymousDonor
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -- BenjaminFranklin, Historical Review of Pennsylvania, 1759.