After the September 11 terrorist attacks, Osama bin Laden argued that Al Qaeda was perfectly justified in killing all those people inside the World Trade Center because they weren't r:eally civilians–they were complicit in U.S. might and misdeeds. Didn't their taxes fund America's CIA assassinations and war planes? As every American understood perfectly well at the time, the attack that day would not have been justified even if all office workers in the Twin Towers had voted for a president and supported a military that perpetrated grave sins in the Middle East. Or even, indeed, if they were all subletting spare bedrooms to U.S. soldiers.
Killing civilians is wrong, no matter how often those who do it insist that the humans they killed weren't really innocent. Everyone understands this truth when the civilians being killed are one's countrymen or allies–but forget it quickly when the civilians are citizens of a country one is fighting or rooting against in war, even though the civilizational taboo against killing civilians becomes no less important.
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:)