But it isn't a loophole. Why has the popular press siezed upon this. It's just normal - it's how different tax jurisdictions interact.
A loophole is an unintended consequence. This is how it goes. A short, thin, balding and bespectacled (STBB) lawyer/accountant will find a tiny bit on the footnote of page 458 of a finance act.
He will, for example, have worked out that a simple bit of law that was intended to give legitimate relief for a foreign exchange loss, actually has an unintended consequence. He will think, well a convertible here, a yen derivative there, and that will yield a couple of squillion of tax savings. Bob's yer uncle
The STBB will contact his likeminded friends and they will test the loophole. They will go to tax counsel (another STTB). Then they will "market" the idea. Or, in other words, phone other STTBs that work in banks and multinational corporations. They will sell the tax saving idea and make millions by saving squillions. Now that's immoral.
Using the law legitimately for the purpose that was intended is not immoral IMO.