Because you're either an Australian citizen, in which case the laws of Australia apply to you, or you're a foreign citizen, in which case the laws of Australia apply to you because you consented to them when you came into the country, or you're an illegal alien, in which case the laws of Australia still apply to you and you're liable to be deported. If you came into the country as a child, your parents/guardians gave consent on your behalf.
You don't get to choose. It's a package deal. Either all the laws apply, the good and bad, or you don't get to be a part of society.