For instance, if someone says that alternative medicine fails for n different reasons, would you say that the person is committing Nirvana fallacy or that there is something to say about the fundamental failures of alternative medicine?
The qualitative fault I'm trying to point out is that trying to tax 'rich people' is a failed attempt because no matter how effective you can implement your tax measures, at the end of the day people can move to other countries and your own country starts to suffer more than it benefits from the increased taxes.
It is a Nirvana fallacy if someone says "No matter how hard you try to curb murders, serial killers always keep finding new ways to commit crime", because at the end of the day, if all the serial killers move out of your country to a more serial killer friendly country, you don't actually suffer, you did your job.
On the other hand, in terms of taxes, you don't want your tax paying population to move out or be rendered incapable of producing wealth. That kind of 'equality' is not worth it.