You are putting agnostics and atheists into one basket which makes as much sense as putting you in a basket with the fundies (you sound like a reasonable person). Even if you can't prove a negative, the onus is on the religious to provide infallible proof.
Extraordinary claims require extraordinary evidence.
You're argument is deeply flawed.
Guns could've quite easily made things worse by the same people being stupid enough to loot also being stupid enough to shoot people without good reason. How many people were injured/killed in the New Orleans flooding during the looting?
Just saying that the efficiency is probably less doesn't make it true.
As far as I can tell its a trade up between...
gasoline refining + transport to filling station + losses in internal combustion engine
burn in power station (more efficient that small scale internal combustion engine) + transmission losses (6.5% from wikipedia) + losses in electric motors (less than internal combustion engine)...so I disagree.