IMO Occam's razor ends up here. Electronic voting systems do two things very well: obfuscate the system in a way that is relatively incomprehensible to a layman, and provide plausible deniability in the case of manipulation. Even if manipulation is discovered, you can chalk it up to a "bug" and re-run the manipulated election again. People are stupid, and most ordinary people only want to believe there's malice involved when they've run out of more pleasing cognitive options.
I believe that if this site enumerated all the ways that you can maliciously use computerized vs. paper voting systems, we would show a hell of a lot more benefits to a manipulator than a voter.