Anonymous - I don't think that word means what you think it means
The LNP Govt in OZ quite frankly couldn't find their own backsides with both hands and a searchlight. And proposed legislation like this shows just how far out of touch they are with the reality of "managing" social media interactions.
Most social media account requirements for "real names" are easily circumvented if that's what you wish to do - so legislation like this really only catches the unprepared or unaware. If you wanted to set up to anonymously defame a member of parliament, or anyone else for that matter, then the process is relatively trivial.
Better still, don't just do it anonymously, do it automatically!
Conduct all transactions via VPN / TOR
Set up an appropriately anonymised Twitter / Facebook account outside of your country of origin (international legal exchanges are much more interesting to watch).
Write a bot script -
"Select name of politician/person you dislike from list"
"Append appropriate controversial comment - cross reference to their Twitter feed / Facebook page to see most recent stupid posting / controversial action"
"Append final disparaging remark"
"Repost to anonymised Twitter / Facebook feed"
Rinse/repeat for the political party / etc of your choice.
Preferably include "pointers" to offshore "bad actors" as a potential original source of the tweet / post - SCOMO and Co love blaming off-shore sources.
Sit back - watch fun.