A very important issue to me as you may have gathered from my previous blows is equality.
I believe every vote should count as one, and every vote should only affect the result by one. However this is not the same under AV.
Party A has 50%+1 of the vote
Party B has 30% of the vote
Party C has 20%-1 of the vote
Under Fptp and AV this is a comfortable win.
However, even from an election pool of 10 million voters, under AV party A may have lost with 2 less votes.
So, to recap..at the moment, they won by 20% or 2 million votes...but take two away and they can lose.
Extreme obviously, but it demonstrates my point in the huge swings possible.
It would seem that under AV, a vote can be worth a lot more than one.