On the other hand, the 'nineteenth century technology' of secret ballots is both obvious and simple. It's a shame that people like Vitalik are so dismissive of it.

You can't write smart contracts based on secret ballots. The dream (well, one dream) is to have governance based on an ecosystem of programs that can vote perhaps hundreds of times a second. A lot of democratic procedure is built to work around the limitations of physical voting; this could qualitatively change the way decision-making works.