sydney thousands people rally marriage equality australia second-biggest city melbourne saturday ahead postal survey same-sex marriage could lead legalisation australia one develop english-speaking countries legalise same-sex marriage despite strong popular support back majority lawmakers shadow attorney-general mark dreyfus opposition labor party call conservative liberal party-led government ensure debate turn ugly ahead postal survey next month particularly call prime minister australia speak bile hate speech might see campaign tell rally prime minister malcolm turnbull last week urge supporters opponents same-sex marriage show mutual respect campaign turn increasingly vitriolic nl4n1lb1tj rally organiser anthony wallace activist group equal love say 15,000 people attend event make one large gay right rally australian history police decline estimate size crowd rally annual event year begin end victorian state library mass same-sex wed ceremony hold australians vote several weeks mid-september non-compulsory postal ballot whether legalise same-sex marriage same-sex marriage support 61 percent australians 2016 gallup opinion poll show issue fracture turnbull government damage stand voters six-month low thousands rally gay marriage australia ahead vote