I often think about that idea and how much more comfortable would it be for people that want to vote. For me to vote in the elections i normally have to drive 20 minutes to the nearest booth, then if i'm lucky i will only wait 15 minutes on line and then drive back home, so in total 1h minimum that i take. If i could vote online safely, 5 minutes would be enough. The advantages of your proposal would be the reduction of costs and more people would vote since its easier and they wouldn't waste time. The disadvantage would be the insecurity and the possibilty of manipulation but i think there are ways to counteract that and i think in the future some version of online voting for elections will be possible.