you should read research on deanonymising data. The government lies, they literally introduced a bill in 2018 trying to bam cryptography because some researchers embarrassed them by proving you could re-identity census data.

Idk what planet you live on but the nsw government literally does eugenics on trans people. I had to get steralised to not have all my ID out me all the time and get the right title etc.

You are young, things can change fast the pendulum of tolerance swings back and forth, Whig history is demonstrably false.

here is a reasonable summary of concerns https://www.salingerprivacy.com.au/2016/03/17/census-no-longer-anonymous/

and here is recent research on deanoning datasets https://www.nature.com/articles/s41467-019-10933-3

edit: also defending the census because of overreliance on it is stupid. We should not make important decisions on unverifiable data. If not being on the census means no funding then the funding model is broken, not the person who doesn't want to be recorded. Censuses have historically been used for extremely bad shit, Australia is a nation founded in exploitation and genocide. There are extremely good reasons why certain people might lie or hide.