Here is how the Bloomberg column, by William Pesek, frames the issue, in a column headlined "Billionaires Dig In to Kill Good Economic Idea":
This, after all, is hardly the evil, capitalism-killing idea that's been portrayed. The tax would be on "super profits," or anything over a level deemed reasonable. Under Rudd's proposal, the levy would be imposed on resource-company returns that exceed the rate on long-term Australian government bonds, currently about 6 percent....The public-relations battle is clearly being won by the billionaires. To listen to the miners, Rudd's tax is an assault on Australia's future. No, just them and their monster profits. Rudd is putting Australians first, and good for him.
Think about this -- any profit level above that of a long-term government bond is deemed unreasonable and qualifies as a "super-profit" subject to a punitive 40% tax rate. It's the government deciding how much profit a company should make, rather than allowing the profit level to be decided by the market of customers for a company's products and for the products of its competitors.
The Bloomberg column frames this as an issue of "billionaires" and their "monster profits" but that's a straw man. I have an investment in some Australian mines through an investment in an American publicly traded company, Leucadia National Corporation, and I am (alas) nowhere even close to being a billionaire.
Here is how the Financial Times editorial frames it:
And applying the tax to mines already in production must be done with great care, ensuring the government's contribution to costs incurred in the past is as generous as for projects not yet started.
Such consistency is necessary – and for a wise government, attractive – to calm investors' fear of a raid on profits after they have borne the whole risk and capital. But it is hardly a moral principle. No country, except those too poor or weak to have a choice, accepts that the government has a duty to compensate those it taxes for the inconvenience of higher rates.
Think about this -- the FT view is that ex post facto law is undesirable for practical reasons as opposed to moral ones, as if there's no moral principle involved in having a predictable rule of law of the sort that is enshrined in the Constitutional prohibition on ex post facto law. And higher tax rates are described as a mere "inconvenience" as opposed to a factor that might affect the return on capital so dramatically as to alter the calculus on the wisdom of the initial investment.
And remember, this is the FT and Bloomberg -- supposedly sophisticated financial press outlets who target an affluent, educated audience.