The Alternative Vote system is only a small change, it is a small reform that will make Parliament a little more representative of the views of the public and make more people's votes count. At present most people's votes make no difference to the outcome of a General Election.
Look at the people who oppose the Alternative Vote. It is the political elite opposing even slight reform because they want to keep control of things as they are. An elite funded by big business tax exiles.
If you look at the people who oppose AV you really should want to vote for it – and vote to end a system where most people do not have any real say over who runs the country.