The principle of one person, one vote is a simple one, and one that nobody really disagrees with; nobody's vote should carry more weight than anybody else's - in other words, every vote should count. I'm somewhat surprised that those campaigning for first-past-the-post as opposed to the alternative vote are using this principle to back their views - because FPTP does not deliver it whereas AV does.
In FPTP, the only votes that count are those for the winning candidate, which is very often a minority. It means that the majority of people's votes don't count at all in the final result. Whereas with AV, every vote counts. If your first choice candidate is ruled out, your vote still counts, because it's transferred to your second-choice candidate. Thus the result of an AV election takes account of every person's vote, whereas many FPTP elections result in most of the votes not counting at all.
The FPTP (no to AV) campaigners say that those supporting minority parties get a greater say in AV, that their votes get counted several times over, that AV is unfair. This is tosh; under AV every person's vote counts once, no more and no less. No one person gets more choice than anyone else, nobody's vote counts for more than anyone else's. Under AV, votes for losing candidates get transferred; but a transferable vote is still one, single vote, and doesn't count for any more than anybody else's vote. Failing to transfer that vote would mean it would no longer count - that voter's choice would be ignored completely - and that is undemocratic.
So let's make every vote count, precisely once, no more and no less: vote yes to AV in May.
