There is no inherent morality attached to paying taxes. And there is no inherent morality that dictates what amount of tax one should pay. There is a legal obligation to pay taxes, and a moral obligation to follow the law, but there is not a moral obligation to pay more in taxes than what the State requires.
Put another way: there is an intrinsic moral responsibility to not murder, but there is not an intrinsic moral responsibility to pay taxes. One could imagine a country in which there were no taxes, and such a state would not be immoral. And those who lived there and did not pay taxes would not be viewed as immoral. But if this same country did not have an explicit statute outlawing murder, we would still call people who murdered others (e.g., killed for pleasure) immoral.
Given that we are morally obligated to pay taxes strictly on the virtue that a law exists that says "You must pay this tax", how is it morally problematic to determine what you owe under the legal structure that has imposed the tax? Your moral obligation is to pay the tax as it is defined, it is not your moral obligation to pay more tax than the tax code requires.
That seems to me to be an obvious tautology: you owe in taxes what the tax code says you owe. If the tax code allows you to limit your tax responsibility by moving money through trusts, so be it. It doesn't seem any different than parts of the tax code that limit your tax responsibility for buying a home, having kids, or making under a certain threshold of money.
Whether or not the tax code, as constituted, is fair, equitable, desirable, or is having its intended effect are fair questions. But calling people immoral because they find legally sanctioned ways to reduce their tax liabilities is troubling.
I don't make enough to really worry about these structures, but I can guarantee you that if I did I would do whatever I could to reduce my legal tax responsibility.