> Now, what can the US government actually do to you while you're no longer a citizen depends a lot where you live and whether you care traveling or doing business with the US again
In most western country anything involving a (even local) bank will be a headache already when you're an American citizen. I can't imagine it would be easier if you're a former American citizen with a large debt towards the US.
The US is a bully because wealthy people want to live, work with, have assets, or even have citizenship in the US. The US is very business friendly and offers top-tier everything if you have money.
Wealthy people though are accustomed to having their cake and eating it too, so naturally they will try to take as much as they can while giving back as little as they can manage. Their wealth will carry them very far towards this goal, so the US cannot be soft when it comes collecting.
Its like saying you need to be hard on terrorism or drugs problems, so that you can actually fix that. We know how that worked in past 100 years...
What it will collect is totally negligible in US budget and won't make dent in anything (compared to say companies like Apple or Google skimming paying taxes by tens of billions yearly), and it won't make many friends to US.
But sure, chase them, chase them hard, I have literally no skin in that game. I guess as long as really serious problems are ignored government is happy.
In Switzerland, almost no bank wants to deal with you if you have US citizenship. Its easier to just avoid creating whole new department for that reporting, risk getting sanctions if you make a mistake etc.
US in this case is a global bully, based on some talks with people involved in such processes also arrogant, very aggressive in enforcement, at the end punishing its own citizens just because they can.
Their choice, but if I or my kids would ever be in the situation of potentially gaining citizenship or green card (that probably won't ever happen, life here is much higher quality overall for people like me), this alone is good enough reason to not do it.