The problem isn't just the taxing, you spend several days each year trying to report correctly the fact that you don't owe anything. If you make a mistake, the consequences may be quite severe, so it's safer to hire an expert. Outside the US, experts on US tax law don't grow on trees, so you spend a lot of money on this.
By the way, you speak of giving up citizenship like it's a small thing. Once you do this, you can never get it back.
'US Persons' in the context of this law is not the same as US citizens. It may include family members or business partners of citizens, or even of family members of former residents. It even affects many people who have no personal connection to the US, in some cases even people who have no right to enter the US without a visa if at all.
Fatca requires financial institutions to find and report any such US persons among their customers, and report their details to the US. This can be problematic, not just because so many US persons aren't even aware they are considered US persons, but also because in some countries banking privacy laws make it illegal for banks to record such information of their customers. These banks are now torn between following their local law and following US law. As a result, just offering certain services to US persons may carry a significant risk.