The argument "Taxing the rich is a bad idea because they'll just avoid the tax" doesn't make a case for capitalist policies.
There are basically 2 options:
If you agree that wealth should be more equally distributed then raise taxes for the upper 0.1% of wealth. It's a relatively easy change and if, like some people imply, it doesn't work then a government can start working on a more involved law which effectively taxes income where it should be taxed.
It doesn't really matter whether you think a simple tax code change will be effective. If you consistently support a government that wishes to equalize citizens it will keep working to achieve this goal, even if simple measures fail.