Firstly I am highly suspicious of the 'it's all terrible simple' bland message I am hearing from some AV supporters (mainly the ones who don't know me, and think that type of tactic will work with me). There are obvious complex issues raised by the new system, which are ripe for exploitation by political hucksters, and the 'Nothing to see here, move along, all very simple' talk makes me baulk. There is much I don't know, but I do know there is complexity here.
Secondly I think these same political hucksters are pressing the new system because it enables the very tactic which they are using in this debate. That is, a PR-type simplified smiley-face marketing message for the populace, with all sorts of shady backroom negotiation.
Thirdly, people in the 'Yes' camp talk a lot about how it is wrong for a party to run a government without majority support. It seems to me there are two possibilities. One is that a particular political platform has majority support among those who vote. In this case AV is not a superior way of ensuring the transfer of power. The second is that there are multiple platforms, and each has minority support. In this case it is wrong to manufacture a spurious majority for one of those platforms by counting up mild preferences ('UKIP better than BNP - I guess') as if they were a full endorsement on an equal footing with those who actually voted for the UKIP platform.
And more concretely I think that if AV gets through a particular tactic will be cold-bloodedly used to enable right wing policies which would not get the support of the majority, and further strip away some of the things which make this country tolerable. I'll post that separately.