I don't agree that doing something for the money makes it unethical. Don't most people work to make money? Otherwise everyone would just volunteer. And not everyone has the luxury of loving what they do.
As for defence force. Look, we are lucky to live in a country that is safe and doesn't need defending (for now). But if we didn't have an army/navy/Air Force, we would be vulnerable to invasions and attack, particularly seeing as we have bountiful natural resources, a tonne of land, and a small population of people who don't have guns.
If you have an issue with the defence force, is this exclusively for Australia or generally speaking, globally? Some countries would not exist today if they didn't have a defence force. Israel for example.
ETA - and I imagine Europe would look quite different too post-holocaust if there had been no force to be reckoned with...