The only difference between an argument against a tax reduction and an argument in favour of a tax raise is what you consider to be the status quo.
The situation is more symmetric than you think.
Greater capital mobility cuts both ways: when you lower taxes you can also attract more rich people and their capital.
(I am not saying that this effect will necessarily occur, only that capital mobility comes into play both when raising and when lowering taxes.)
Oh, of course, the real solution to these problems is to tax land and not income nor capital: you can't hide land nor can it leave the country. See https://en.wikipedia.org/wiki/Land_value_tax
The situation is more symmetric than you think.
Greater capital mobility cuts both ways: when you lower taxes you can also attract more rich people and their capital.
(I am not saying that this effect will necessarily occur, only that capital mobility comes into play both when raising and when lowering taxes.)
Oh, of course, the real solution to these problems is to tax land and not income nor capital: you can't hide land nor can it leave the country. See https://en.wikipedia.org/wiki/Land_value_tax