I am opposed to the adoption of AV. One of the main reasons I am opposed is that most of the people who will use it (including many of those who support its introduction) don’t understand the system; whereas nearly everyone on Earth understands FPTP. Call me “a conservative Right-winger who hates any form of change”, but I think that it is fundamental to the legitimacy of a democratic system that its voters know what their votes mean.
Predictably, commenters are ridiculing this, on the grounds that how you vote in AV is really very simple. This misses the point.
AV's defenders tend to misunderstand the "complexity" complaint. The problem isn't that it's too complex to understand how to vote. The problem is that the relationship between the vote and the result is complex enough to allow people who've studied the system to make their votes count more than other people's. And that's fundamentally antidemocratic.
Plus there's an instinct problem. Give people a list of candidates and tell them to list them in order of preference, and they'll put a number next to every name. People don't like leaving blanks. This is why Facebook do so well: stick a form on the site for "favourite music" and users will list all their favourite bands, despite the fact that it's a completely pointless thing to do. AV by the nature of its design abuses this fact of human psychology to give large numbers of votes to candidates no-one actually wants. And it is deeply counterintuitive: putting a candidate twelfth out of twelve is understood by everyone to mean "Worst — do not elect", but AV treats it as a positive vote to be counted in that candidate's favour. Which comes back to my first point: the few politics junkies who study the system will know this, enabling them to make their votes more valuable than everyone else's.
That AV's voting instructions are so simple to follow is the very problem: the system is so simple to use that its complexity isn't apparent to users — and, if people don't know the complexity's there, they won't try to find out about it. A system that was more obviously complex would actually be an improvement: it would be honest.