[lucideer]

I think the sentiment of the OP actually gets to the heart of this (the idea of open-source is transparency, visibility, auditability) but the problem here is it need to be applied to the actual process, not to the process of building tools for the actual process.

It's not that developing voting software should be open-source, its that actual voting should be "open-source" in the physical sense.

Trusting the system is possible if you can (you, yourself) readily observe every part of the system. I don't think giving members of the public access to the server your voting software is hosted on is a very viable idea, but giving members of the public access to paper count centres is (it's done very successfully in many countries).