They think it attracts pedophiles.
Because, god knows that taking away images of adult women they can masturbate too won't encourage them to look for kiddie porn or anything.
I wonder how this makes small breasted women in Australia feel - since it's sorta telling them that their husbands and/or boyfriends are potential child molesters. It's also sorta saying that they are not adult women if they don't have big tits.
Oh.... and has Australia not heard of the fucking Internet? Because, good fucking luck trying to block every website in the world that features chicks with itty bitty titties.