Important to understand that the right to expatriate / renounce citizenship in accordance with the law is not just some dodgy workaround which might or might not succeed. It's US law. There's nothing to be pursued about, and no need to be scared.
I believe the above is correct but incomplete, in that this will succeed in eliminating any US tax liability under US law on income earned outside of the USA after the expatriation date.
That is mostly(+) true even for a person who owed some US tax, according to US law, before expatriation. [(+)there may be some exception for "covered persons"]
However, this does not address the issue of potential US tax liability on income earned and assets accumulated before the expatriation date. Here, it's clear (under US law) that the person is liable to tax. On the other hand, there is an important practical ambiguity around enforceability.
Technically speaking, per US law on its own, there is no ambiguity around this: US law as written has no geographic limits. It applies to any US citizen, anywhere in the world, as well as any US green card holder and any US resident. All such persons are taxable as US residents under US law for the period during which their citizenship/green card/residence status applies.
What creates the practical ambiguity is enforceability. if a person has no US assets, then the US government depends mostly on the willingness of their country of residence to help with enforcement, which may not be very high if the rules are seen as unfair. I say "mostly" because the US has an additional big stick, and the US uses it: most global banks need to operate in the US financial system. FATCA is a tool by which the US uses that leverage to make non-US financial institutions help the IRS with enforcement: to keep their US license to operate, they agree to either kick out US clients or send their personal financial information to the IRS. Most of the bank letters are intended to give the banks legal permission to send that information, so that the banks cannot be sued by their clients for following the US-imposed rules.
Until now, as best I understand it, the information exchange has been the extent of enforcement on non-US residents related to FATCA: the IRS gets a bunch information from banks around the world about people's accounts and income. There is only a practical consequence if the IRS is able to do anything with the information, which in most cases seems unlikely to happen.
As I see it, the risk being taken by a person who renounces without jumping through all of the IRS hoops such as filing tax returns and an 8854, and potentially paying an exit tax, is that the USA could, in the future, develop and implement additional ways to ratchet up the enforcement, for instance by changing the legislation so that US Border Control checks incoming visitors against information the IRS got under FATCA. Or, they could sign new agreements with non-US financial institutions that require said institutions to withhold money from the accounts of their clients who are or were US persons, or face loss of their license to operate in the USA.
That very sounds far-fetched today -- but 15 years ago, who would have predicted FATCA? 9-10 years ago, just after FATCA passed, who would have predicted that FATCA-like information exchange among all Western countries would become the norm? Yet, both did occur. Also, with aging populations, Western countries need to raise tax revenues, and the most politically acceptable manner to do that is by enforcing existing laws. Now that countries other than the US have something to gain from this trend, it could accelerate.
Going through the whole process with belt and suspenders, i.e. paying the lawyers and accountants to do everything by the book, is like buying an insurance policy: it means that even if the rules and the enforcement practices are changed, there is not a stored-up problem that could re-emerge in the future. The cost of that insurance policy will vary, depending on the cost of the specific lawyers/accountants and on whether there are any associated US tax liabilities. The potential benefits will vary as well, depending on the individual's level of assets and income, need to travel to the US (or not), wish to invest in the US (or not). Finally, individual risk tolerance must play into the equation.
A risk-averse individual who qualifies for the exemption, travels often to the USA, owns a house in London that they bought 25 years ago, holds a sizeable investment portfolio, and has paid plenty of UK tax on their gains and income, may find that this insurance policy is "good value" relative to its cost: they lock in the exemption for a few thousand dollars in accountant fees without paying any meaningful amount of US tax, and thereby eliminate a source of worry and a potential US tax liability in the hundreds of thousands.
A person with more modest assets who has nothing to do with the US and feels the rules are totally unfair might find the compliance costs are so high it's not worth hiring the lawyers/accountants.
Finally, a risk-taking UK-focused entrepreneur who does not qualify for the exemption, has a large house in London and a large investment portfolio, and would hence be liable for a large exit tax, might decide to solve the immediate problem with local banks by expatriating, but take the longer-term risk by refraining from filing anything with the IRS and hoping that the rules or their application will not change meaningfully in the future.