I think it's a combination of things. What you mentioned above factors in a lot, as well as the "sheeple" thing. However, I think it's also a "what has science wrought" fear, too.
If you look at it, most of the great archetypical fears of Western culture play upon science gone amok or science more advanced than we can comprehend - AI, genetic engineering, aliens, dystopias, etc. Many types of zombies play into that same theme - they are created from science gone wrong. A lot of it strikes me as a fear that humans are meddling in things we should not, and that one day we will step over the line and cause out own demise. I'm not saying this fear is logical, but it certainly is out there - look at all the fear stemming from the large hadron collider earlier this year.
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If you look at it, most of the great archetypical fears of Western culture play upon science gone amok or science more advanced than we can comprehend - AI, genetic engineering, aliens, dystopias, etc. Many types of zombies play into that same theme - they are created from science gone wrong. A lot of it strikes me as a fear that humans are meddling in things we should not, and that one day we will step over the line and cause out own demise. I'm not saying this fear is logical, but it certainly is out there - look at all the fear stemming from the large hadron collider earlier this year.