Seeing the Forest makes a good argument for why we need paper-trail voting machines.
I'm supposed to touch a screen and then just trust that the machine correctly records my vote. Right.
Suppose that every computer expert in the world decided that the machines were beyond any possibility whatsoever of being tampered with. (Set aside for a minute that it is the computer experts - the people who understand computers - who are sounding the warnings about the possibility of fraud from these machines.) And suppose that every politician, every authority figure, every credible organization declared that these machines are beyond question. Suppose that even every "fringe conspiracy nut" in the world issued forth with assurances that the machines accurately recorded votes.
There is still a problem. You still can not prove that the voting machine correctly recorded the way I voted.
Take a look. The entire thing is worth a read.