It turns out you can write to the Prime Minister via an online form, Roger Lamb pointed out to me and others via Twitter. Here's what I wrote:
Policies that will make me not vote Labor
Dear Prime Minister
Congratulations on your accession to the office. I am impressed that you eschew faux religiosity and do not apologise for your marital state. It's about time we had such honesty in our politics. But I wish to express my concern, both as a voter and as an academic (I teach philosophy at Bond), about some existing Labor policies and statements you have made in recent times
1. Internet filtering: this is a regressive and paternalistic policy that will, incidentally, not work. Drop it immediately. I would also suggest that Senator Kate Lundy is a good person in this discussion. That is, if you are unable to appoint Senator Ludlam to the ministry.
2. Gay Marriage: Some 10% of Australian citizens or so are discriminated against. You may not like gay relationships, but they deserve the same protection of law as every other citizen.
3. Asylum seekers. Must we really defer to xenophobia here? Asylum seekers are a minuscule problem in population growth (and you have adopted the right slant on that matter); say so and make the process more humane.
These policies as they stand are deal breakers for me. I know they are deal breakers for many others who might be classed as "swinging voters". You won't change the minds of the entrenched, but you can for those who are social progressives, who were once the constituency of Labor.