The problem used to be that we only had an M15 rating for games in australia and when we finally got an R18 rating we thought that would be it ,but the sticking point is the guidelines that state your game cannot promote or incentivise drug use or sexual violence , why this on the surface seems reasonable given their argument that it is an interactive media , the problem is the strict definition .
Seems like you're reaching a bit to defend something that is indefensible.
A government banning the sale of art is something you'd expect in unenlightened countries, or at least in those with more authoritarian regimes.
At the very least it should be permitted for adults to purchase the game... any game... ever. And Australia is infamous for this reason internationally.