I didn't say that paper elections cannot be rigged. They can, and have been more often actually than there have been fair elections.
I did not even say that it's easier to rig electronic elections than paper elections. Personally, I'd expect it to be as long as you're the one calling the shots.
What is harder is simply to debunk cries of foul play. People can easily imagine what a paper election is like and how counting them (with representatives of all parties involved present) can be somewhat trusted. It is easy, on the other hand, to convince people that this is not the case with voting machines.
People don't trust what they don't understand. And trust is something a democracy needs urgently. People need to have faith in their system of government. Whether they like their current government or not, but they need to know that it was elected fairly and that it is what "the people" wanted. That's the whole problem here. Because without