> (2) Slot machines are already protecting millions upon millions of dollars from countless people who would love to be able to modify those machines' behavior.
There difference is motivation. If a slot machine pays out too much, the company that makes them won't get any more business. If a voting machine favours certain candidates, those candidates benefit from letting that continue (if they weren't instigating it to begin with) and often they might have been the ones in power when they voting machines in question where chosen.
> (3) A backup-paper trail would reduce error and allow for recounts. You vote, a receipt gets printed, you confirm that the printed paper represents your vote, and you're done. (The paper stays with the election commission)
This I agree with, and it would satisfy most concerns with electronic voting if you combined it with paper recounts of some random districts and, say, and districts with small margins or unusually large shifts.
Focusing all that much on the security of the voting machines is a sideshow, IMHO. You need some level of security, but pretty much any security mechanism you introduce will be inferior to recounts based on receipts collected using tried and true methods of paper, sealed boxes and independent observers.
Focusing on a solid recount solution that includes rules for when to trigger automatic manual paper recounts won't just catch malevolent interference with machines but also reduce the chance of problems due to bugs, hardware and software failures and all kinds of other problems.
But of course it'll cost more than switching to a purely electronic system, and that extra money won't go in vendors pockets.