Indeed, a very hot topic for some.
A discussion of renunciation of US citizenship, whether Boris Johnson or a lab technician living in Vancouver, should not be generalised. Discussion of the consequences of US income tax on Americans living abroad, also, should not be generalised; especially when it concerns retirement planning and US citizens living abroad on retirement income.
The massive variations which may alter one's perspective:
Is the retirement income primarily US source, or foreign source?
Has the individual lived most of their lives in the US or abroad?
How closely does the individual guard their financial identity? Are they comfortable using personal financial information online, or are they more guarded about public exposure of their personal financial information. Nothing sinister here, we're not talking about people actively evading tax; just ordinary people doing ordinary things like having a bank account or taking out a mortgage.
What foreign country are we discussing? For US tax purposes combined with foreign residence, some are more difficult than others (Switzerland and Germany, for example).
What will the individual's ties to the US be once retired? Family? End of life planning? None?
A difficult and emotive subject (believe me on this, I'm going through pragmatism versus emotional ties at this time on this very subject). BTW, Boris has settled with the IRS (and no, no one knows the outcome) and has yet, as far as anyone is aware, to renounce.
This is a topic best left for discussions between adults, especially those with no "hobby horse"** ideals.
***This is not about patriotism, love of America, or greed. It is about the engineer living in Sydney, the lab technician living in Vancouver, and the secretary living in London, or the retired executive living in Houston considering partially relocating back to the home country during retirement
) Alan and I, amongst others on this site, have been part of similar discussions before on other expat sites). It is not about Eduardo Saverin, Denise Rich, or indeed Boris Johnson.