Taxation is at the heart of what makes the state possible, and it's the state, as a guarantor of justice and peace, which makes creating and keeping wealth possible. The wealthy benefit more from this arrangement, and it's fair that they are taxed more as a result. I presume you're not arguing against the existence of the state, or the need for taxation for its upkeep.

Given the need for taxation, making taxation fair requires information about economic transactions. But there's a balance to be struck here: having the state be informed about the details of every transaction, tied to each individual, would probably be too dangerous for liberty. But on the other hand, lack of oversight will lead to evasion and free-riding. So it seems that it's best to put effort in investigation in proportion to detecting potential free-riders.

Large amounts of money held in opaque arrangements abroad would seem to me to have a high probability of abuse; and with the numbers of people involved being small, the instrumental loss of liberty in having these arrangements investigated seems to me small compared to the free-riding risk.

I also object to the argument you've used; it gives me a slimy feeling reading it. You've tried to drag in this notion of privacy and respect by association with "professionals", attorneys, priests and spouses (!), to what amounts to hired thugs protecting a box of valuables. Banks spend a lot on appearances because they need to give their customers the impression that they're safe places for their customers' money, but at the end of the day, they're out to extract as much of that money as they can. Banking isn't a respectable business, particularly these days. They're a necessary part of the economic infrastructure, a bit like water supply and sewers are to cities.