Evil Patronus - ties into Snape's Patronus

[crypticamoeba]

No: HPFGUIDX 140972

 
Perhaps this has been discussed before but what evidence is there that 
an evil/dark wizard cannot preform a Patronus Charm?  I have seen 
several arguments/theory that state if Snape can produce a Patronus or 
send the order a message via the PMS (Patronus Messaging Service) that 
DD invented; it could prove that he is DDM!Snape.  
 
>From PoA Chapter 12:
 
Lupin continued, "The Patronus is a kind of positive force, a 
projection of the very things that the dementor feeds upon -- hope, 
happiness, the desire to survive...
<snip harry stuff>
"With an incantation, which will work only if you are concentrating, 
with all your might, on a single, very happy memory."

Going via the necessary emotions -- hope, happiness (not necessarly 
pure or good intentioned), the desire to survive -- is there anything 
that could say Voldemort could not preform the charm?


crypticamoeba