It's not straightforward at all. There are a bunch of financial implications that are very difficult to navigate.
It's expensive to renounce US citizenship.
You mean if they've been living and working for years in the US, and taking advantage of US tax-advantaged retirement accounts?
Now we're talking about a different person than the parent commenter: "(loosely defined as people who were born in the US decades ago) who do not live or work in the US "
> * Your average annual net income tax for the 5 years ending before the date of expatriation or termination of residency is more than a specified amount that is adjusted for inflation ($147,000 for 2011, $151,000 for 2012, $155,000 for 2013 and $157,000 for 2014).
> * Your net worth is $2 million or more on the date of your expatriation or termination of residency.
> * You fail to certify on Form 8854 that you have complied with all U.S. federal tax obligations for the 5 years preceding the date of your expatriation or termination of residency.
This applies to a tiny subset of people who are either a) Extremely wealthy, or b) Already tax deadbeats.