[kartan]

The problem is complexity and trust.

For the first, even the most tested software still have bugs. Politics is already a complicate business if you add bugs. Complexity also affects trusts. It is easier to trust a system that you understand like paper voting than trusting machines that, for most people, look like magic.

For the second, the problem is that if I can't count the votes I have to trust the good will of the company that made the machine or some selected technicians that review it. The Volkswagen scandal is a good example of how things that can go wrong. You can still manipulate results in paper voting, but usually requires a lot more of people involved and because that it is easier to detect. Mass manipulation is easier to do and harder to detect if there is no paper to count.

So both solutions a the same time is the best of the two worlds. You can have a machine that counts the votes and still prints a ticket. So you can have instant results, better counting, etc. And this results can be checked if any doubt arises. (I will say that will be good to check them always anyway). So you can detect easily bugs or manipulation.