That works once, then it stops working in the future and backfires because people would no longer be motivated to create wealth in that jurisdiction. Which means no jobs and no tax revenue.
Occasionally people do leave, whether for tax reasons or other reasons, but on the whole even the wealthy agree that the quality of life you get from living here is worth the expense paid in taxes, compared to moving somewhere that's more unequal and more violent. If anything I would guess there is a net influx of well-off people, and there would be more of one if immigration rules were loosened, to make it easier for wealthy people to move here from outside Europe.
For Denmark, about another 7 years. Why do you think the government is acting the way it does? (For those not familiar with the situation, pursuing a reform strategy in straight opposition of explicit pre-election promises). By then, the baby-boomers will have retired and the smallest generation in modern history is left to pay for everything.
As for crime, there is no evidence that low inequality causes low crime rates, or the opposite. Significantly more inequal Switzerland and Singapore has lower homicide rates.
This study disagrees: http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s...
Imagine, if you were a multi-millionaire, would you go to a job you hated for 60 hours a week?
It certainly can have adverse affects on investment payoffs that distort market logic; if you could figure out a way to progressively tax consumer consumption instead of income you could get around that.
Singapore, being a rich island nation, works the same. If they started taxing the shit out of their rich it would certainly result in many of those people leaving the country and many, many more not setting up shop their in the first place.
Hong Kong and Singapore thrive because they are low tax, low regulation havens for the rich. Start enacting 'eat the rich' policies and the rich will go elsewhere.