I don't think that analysis holds up. Optional preferential voting is closer to first-past-the-post than compulsory preferential (in Queensland and NSW where t

I don't think that analysis holds up. Optional preferential voting is closer to first-past-the-post than compulsory preferential (in Queensland and NSW where they have OPV at a State level, a large majority tend to "just vote 1"). First-past-the-post is bad for minor parties, and would cement the two-party system. At the last election, the Greens only won the seat of Melbourne by using Liberal voter preferences to overtake the ALP candidate, and similarly Andrew Wilkie relied on the preferences of Liberal, Green and Socialist party voters to eventually win from third position. Under OPV, it is highly likely that both of those seats would have gone to the ALP. OPV might be defensible on the grounds of reducing informality, but it would push our system closer towards FPTP and be bad for minor parties.