If electronics is involved in the act of voting, the voter has no assurance that the ballot remains secret (even if you're a software engineer!). With paper/envelope/box, by contrast, the voter can see and understand the full process.
This is a solved problem in India [0] - and the system is brilliant in its simplicity[1]: Fixed function non-reprogrammable battery operated electronic units, no connectivity, randomization of voting units and a paper trail for verification.
