MELBOURNE, Australia — Australia’s defense minister on Wednesday won a defamation case over a six-word tweet that called him a “rape apologist.” Critics and experts said the court case exemplified the conservative government’s heavy-handed approach toward regulating damaging commentary on social media — what Prime Minister Scott Morrison called “a coward’s palace.” The case also represented a troubling shift as politicians bring more lawsuits against ordinary citizens, they said. The dispute began when Shane Bazzi, an advocate for refugees who has 13,000 Twitter followers, wrote a Twitter post in February about Peter Dutton, then the country’s home affairs minister and...