I have to admit....the urge to get rid of someone obviously evil is very great, however...like lurkette said...who knows what would happen, even if you did...a butterfly flapping its' wings on one side of the earth can, amazingly effect change on things...just as a pebble thrown in the "cosmic pool" can change others....
I guess this really boils down to where you believe thoses changes lie...are they predetermined? (i.e. if someone killed Hitler, WWII would not ahve happened, the world would be a better place as millions would not ahve died) or (i.e. if someone killed Hitler, WWII, in this sense would not have happened, however, WWII(b) would have...and the repurcussions of which are unknown...)
To answer the question...I dont think I would kill anyone as doing so would create an anomaly in space/time that might ultimately bring more disgusting and evil acts into the present.
...interesting qestion...
(BTW...the removal of the other boards has really made me realise what a great bunch of other boards there are on this server....a forum that makes me think...it has been a long time
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