Military Expert: The World Could Never Survive a Real 'Battle: Los Angeles'

From "The War of the Worlds," "Independence Day," "Transformers," "The Day the Earth Stood Still," "V" and the current box office favorite, "Battle: Los Angeles," alien invasion is most definitely part of our culture -- and maybe our fears.
But, in the real world, if predatory ETs come to Earth to take us over, for whatever their reasons, could we, in fact, prevent it from happening? Could we actually survive such an attack?

Scene for War of the Worlds

"The bottom line for a hostile engagement between aliens and humans is not a pretty picture, and there is no happy ending for us," according to John Alexander, a retired Army colonel who spent 25 years searching top levels of the U.S. government for evidence of a reported UFO cover-up -- and couldn't find one.
"We know how we and animals respond when threatened -- they don't try to negotiate, they attack and defend themselves. If we're supposed to be above that, then it ought to be handled a little bit more cognitively."
From a strategic point of view, Alexander suggests that invading aliens wouldn't simply "resort to fighting our military forces directly" when there are so many easy ways to accomplish that mission.
"If they chose to use physical force, they would simply destroy our infrastructure, power, communications, transportation and economic systems. While a terribly blunt approach, it could be accomplished without any danger to the aliens, or direct confrontation with any military system."
"If depopulation of Earth is an objective, the simplest way to accomplish that would be to introduce one or more biological organisms that kill humans.
"There is no reason for them to engage in the time-consuming effort to physically eliminate the armed forces of Earth. Biological warfare would be the most efficacious, energy-efficient and safest means for them to conquer Earth. For the aliens, this is a no-risk option."