The majority that voted. Those in favor were more likely to go out and vote than those opposed. Many of the opinion polls showed that more people were opposed, but clearly not enough of them actually went to the ballot.
Either way, I'm confident that the same measure today would have a snowball's chance in hell of passage.
That's the way democracy works, though. If about 320,000 more conservative voters had turned out to vote in several swing states in 2012, we'd have a different President in the White House.
That doesn't mean Romney should have won, though. It's the people who turn out to vote who get to decide. If you don't care enough to vote, tough beans!
I don't think anyone is disagreeing with that. The point being made is that the people who come to vote are the ones who make the decisions. If people are being prevented from casting their votes, that is a serious problem, but if people choose not to exercise their right to vote then whatever vote they would have cast doesn't count towards the outcome.
Saying that a vote would have gone differently if more people on the losing side voted is obvious. It's also not constructive, except in the context of wishing more people would participate in the political process in the future. Amusingly (or perhaps not), the fervor against Brendan Eich is based in large part around his participation in that process.
I agree that in practice elections are won by those who manage to cast their ballots, but I disagree with the notion that this is not a defect but rather how democracy ought to work.
I'm all for the option to not vote, but I want it to be a choice. I think the current setup provides the wrong incentives: it encourages politicians to care about how they can rouse up enough to come to the polls or demoralize enough to keep away, in addition to or at the expense of reaching out to all constituents. We can change this either through cultural or legal means, but the legal way is faster and not demonstrably harmful.
Greater participation is far from a panacea, of course. It may even introduce its own particular ills (e.g. takes longer to change the status quo). But I hardly think it would make no difference at all. That's why I pointed to other democracies with better voting records, to show that overall democracy isn't harmed by more voting.
Either way, I'm confident that the same measure today would have a snowball's chance in hell of passage.