FATCA is utterly bonkers though.
Taxes aren't a payment for services rendered.
If your girlfriend doesn't believe herself to be an American she should renounce citizenship. But you are asking to have her cake and eat it too.
As you can read in this thread, it costs over $2,000 to file renunciation, and your taxes need to be in order. Resolving the tax situation in this case sounds quite expensive. Oh, and I think you have to pay taxes for up to 10 years after renunciation, and you can't renounce until you're 18 years old.
Suppose you were born in the US while your British parents were finishing up a college education. You left the US when you were 6 months old. You've not back to the US, you have no US relatives, you don't know anything about US taxes, or Selective Service requirements, or other obligations of US citizens, and have no plans to even visit the US. Then at the age of 40 you realize that you are under US law. You want to renounce citizenship, but learn you'll need to pay $150K in penalties, even though you've been paying UK taxes all your life and would never have needed to pay US taxes had you filed. You only have $50K in savings.
What do you do, and how do you think you would feel?
As long as you maintain a passport and citizenship, how do they not have such a right?
In January, I got a tax refund from the British government, since I'd been paying tax on my income at a rate that expected me to earn that amount for the whole year. Claiming that was the first tax return I'd ever completed, i.e. the first time my taxes weren't correct automatically.
My only remaining "asset" in the UK is my student loan, and some money in an account to make the payments. I do not expect to communicate with the British tax office ever again.
This situation is typical of most countries.
If you ask what moral legitimacy it has, then the answer is none - they have no right.
The UK embeds the cost of consular protection and embassy services into the renewal cost of a passport - approximately £15 in 2010, probably more now. It's an insurance payment that most people will never use, so it doesn't need to cost very much per person.
Citizens of a number of countries can enter the US without a visa. They don't also have to fill out tax returns in the US.
This is certainly not limited to western countries, to underscore your point. Even India evacuated its citizens from Yemen, while the US did not. [1]
On that note, India also organized the largest-ever civilian airlift to evacuate tens of thousands of citizens from Kuwait during the Iraq invasion (1990). [2]
[1]: http://america.aljazeera.com/articles/2015/4/7/us-among-26-c...
[2]: https://en.wikipedia.org/wiki/1990_airlift_of_Indians_from_K...
Additionally, if she has dual citizenship, she would get it for free from the UK anyway even if she lives in Spain.
People with British passports also have 90-day visa free access under the Visa waiver program. Unless she intends to move there, there aren't really any benefits to being a US citizen, and certainly nothing that can justify extra-territorial taxation. She gets no services from the US government.
But if she chooses to retain her citizenship then she's incurring a potential cost to the US, which surely it's reasonable for her to contribute to.
Why is she still a citizen? The article says she's in the process of renouncing. Not done already probably because:
• She might one day need to spend time with family or elderly relatives, even if she'd prefer to stay abroad.
• The USA does not allow you to give up your citizenship for tax reasons. She's probably screwed herself here by talking to the BBC, so I suspect she doesn't know that (edit: wrong, I missed the part in the article where it says Jane is a pseudonym). If they think you relinquished your citizenship to avoid taxes they can simply levy taxes on you anyway.
• Giving up citizenship is itself an expensive process and can trigger an "exit tax" that assumes you liquidated every asset you own on the day of renouncement, including things like a home. This exit tax can itself make giving up US citizenship financially infeasible.
• It costs $2350 and can take months.
In short, the entire US FATCA system is designed to screw over expats as hard as possible. It's very hard to get out and isn't at all justifiable under any moral or ethical code I'm aware of. The only reason the US can enforce it at all is the primacy of New York in the financial system and the incredibly aggressive Congress.
I think your argument is a post hoc justification.
Plus, "access to US consulate services" makes no sense. Many if not most Americans living overseas pay no taxes to the US. The complaint is the hassle and expense of filing the paperwork, and the likelihood or at least worry about exorbitant fines.
Finally, who do you think uses those services more - American tourists and business people, or those who live in the country?
Elsewhere leoedin points out that 'The UK embeds the cost of consular protection and embassy services into the renewal cost of a passport - approximately £15 in 2010'. That sounds like it's more equitable, and it shows that consulate services are not expensive. I pay 20x that amount for my accountant to deal with my US taxes, and would gladly play a flat $100 "I live or travel overseas" fee instead.
I am still failing to see what rights, if any, they actually get out of this arrangement. The right to vote ... except that the only issue that concerns them is the treatment of expats, and expat votes are spread around all districts meaning they are essentially ignorable. Not worth anything.
Ostensibly, the fees were raised as a reaction to Eduardo Saverin's expatriation for tax avoidance purposes.
Congress is to blame for plenty, but not this.
The embassies is also for people just traveling/visiting and not living permanently abroad.
My wife has those! guess what we don't pay a dime because we are citizens of... the rest of the world.