What hasn't been mentioned in all of this is that the use of machines for voting is closely related to the widespread effort to make sure that people who -- for one reason or another -- can't actually write down their choices still get to vote.
Think about it.
Ever hear of JIM CROW?
To make functional literacy and legible handwriting (of English) a prerequisite for voting would "dis-enfranchise" certain voters (mostly those who vote Democrat, it would seem).