Froggy Slayer said:
Some extra info; these aliens aren't trying to exterminate us, they instead want to break our spirit. They are desperate; their home planet is extremely overpopulated and invading ours and replacing us (except for a few downtrodden dregs, kept as a warning to any species stupid enough to mess with them) is their only hope for survival. They are therefore unwilling to use the most destructive WMD's such as nukes, as they want the planet to be relatively pristine. Before you say anything, the transport vessels have good point defence, so we cannot just know them out of the sky. They are also willing to use much nerve gas.
Crap, so now we not only stand the chance of being wiped out, but we also face the humiliation of being defeated by a society too stupid to control their own population and properly manage their own resources? Humanity could be forced to hand over the earth to creatures who will likely use it up and perpetuate their own desperation? Kill them all.
As far as human vs human warfare goes, I really don't understand the belief that civilians should be spared from slaughter. Victory comes from the complete depopulation of the enemy country. Anything less just gives them the chance to regain their strength and try again later. Just look at Rome and Carthage. If I recall correctly, they went to war three times. At the end of the third war, Rome starved the people of Carthage within their own walls, then kicked down the doors and burned every last citizen of Carthage, living or dead, in a great pile in the middle of the city. Carthage never attacked Rome again, because nobody was left alive to call themselves Carthaginian.