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As for the second question, I also thought the same thing years later. I also though it would have been more practical to develop combat robots rather try to turn aliens into bio-weapons, although they could have learned from their physiology.
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Combat synthetics would be susceptible to electrical attacks...ie EMP, hacked software, computer viruses...etc.
Plus if they can initiate a weapon behind enemy lines that is self sustaining, spreads rapidly, and wipes out everthing in sight without having to spend billions of dollars to develop it that would be the way to go. That's why current militant forces try to develop chemical, biological, and nuclear weapons as opposed to cyber attacks and robotics. It's cheaper in the long run. Not to mention there's no way to track the origin of this weapon so fear of repercussions is virtually eliminated.