There are several issues here. First, what happens on other articles is not really important. We are talking about the Australian Greens. Second, there is a significant group of editors who dislike simple labels in infoboxes and the like, as these simplify what is often a complex situation. Those editors seem to predominate among the editors of this article. Third, terms like "centre-left" and "centre-right" are pretty broad terms, while "left-wing" is not. The only term that I think really describes the Australian Green in "green". Finally. I note that you have only been on wikipedia for a few days. I suggest that it is best if you do not get into big arguments, but keep a low profile while you learn how things work. It is a very complicated place and even after 6 years it confuses me sometimes. We work on consensus and I do not think you are obtaining that.