Actually, I think most people can imagine that it could be. They just aren't assuming, as you are, that it must be.
I don't understand why any speculation is necessary... Tracking epidemics is a known science and is the provenance of the NCDC. If they aren't already doing DNA analysis of the virus and trying to determine its origin, somebody up there needs to be fired. If it originated in a lab, that should be easily distinguishable from virus found in the wild (presumably in Egypt or whatever other third-world cesspool in which it originated, right?).
But I suppose everyone would rather blither on moronically... What's the problem, is everyone here a Humanities major, or something?