Earlier quoted context omitted.
This is the Nirvana fallacy. Because we can't fix everything, there's no point in trying to fix anything. For example: "what's the point in having seatbelts? People still die in car crashes." The reality is, just like a seatbelts reduce the number of fatalities in car crashes, each loop hole closed makes things a little more difficult for people to shelter their assets.
But at what point, OP's criticism is a qualitative criticism of the approach being advocated? 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 fa…
The first half of this--that rich people can move to other countries if they think they are being taxed too much--is certainly true, but I have doubts about the second half.
There are people who have as part of their drive a desire to see humanity as a whole better off than we were before, and there are people whose primary drive is "eff you, I got mine." That's the kind of rich person who will be the first to abandon a high-tax country in droves, and in my opinion we are better off without them: they are the profiteers who make life for those working under them hellish, who feel no responsibility for polluting and underpaying and ignoring externalities and racing to the bottom. What we want, who we should hope to see become successful, are principled people who understand that the riches which come their way are only possible within the context of a healthy society, and who are willing to part with a larger share of their fantastic revenues to ensure its continued improvement (while of course still being able to enjoy the fruits of their labor).
To argue otherwise, as it looks to me at least, is to argue that (1) the only way to make a lot of money is to be selfish and unethical, and (2) we still need that money in taxes (at a lower tax rate) to maintain a healthy society. I am sure I'm simplifying things.