Faustino,
I certainly agree that there is “a general rule that you should not try to address multiple policy objectives with a single policy instrument” among economists at least. I am not so sure this is understood by non-economists.
With regard to Australia, you might note that the conference were I gave this paper (linked above) was an Australia Day event in Houston organized by the Australian-American Chamber of Commerce. In addition, I was asked to speak at that conference in part because I gave a previous version of this talk at the University of Western Australia last August. The paper has more comments on Australian policy that the summary version above.