|But democracy is (meant to be) all about choice.|
Well, not exactly. Democracy is about choice, yes, but it is also, and I think foremost, about participating. About taking resposability for the fate of your nation, and your people. So, if you don't vote, you're not being "democratic".
Besides, if you are not required to vote, and if authorities don't make it easy for you to vote (by placing election day in a normal working day, thus forcing the voter to sacrifice hir lunch break to go vote, like I reckon is in the USA*), then what you got is that only the people who are really radical about their political views, which mean good, moderate people (the majority of the poplation, I believe) end up under-represented. Which kinda screws the "democratic" part of democracy.
In Brazil, voting is mandatory (there are fines and you're not allowed to run for office or get a passport or a public job if you're behind with your voting obrigations), but you get the day off in election days. Which is quite a sweet deal if you ask me. Go to vote early in the morning, then you can hit the road for a extended weekend at the beach. Woo-hoo democracy!
*and this two parties system of the USA is also very un-democratic, if you ask me, specially if both parties are right-winged. One is moderate righ-wing, the other is radical right-wing, as Gore Vidal would put it. I'd say one in wimpy and the other is fanatic, but that's jut good old cynical me. And this is a whole other debate here