You can see it this way: if you can time people voting, you can hide the camera anywhere in the voting room. Checking the booth is always going to be easier tha

You can see it this way: if you can time people voting, you can hide the camera anywhere in the voting room. Checking the booth is always going to be easier than checking the room. There is also the issue of voters selling their vote. It's pretty easy for them to wear a tracker that tells you when they were in the booth. On the other hand, with paper ballots, the buyer has no way to check the vote, since market ballots are null.