There’s a difficulty with these two parts of the argument:
“But the questions are complicated and perhaps even uncomfortable for those asking them. The relief efforts needed are larger than they should be due to how these countries have been starved of tax revenue precisely because they have chosen to be tax havens.”
“A modest proposal would be for the countries to raise money from the companies by increasing, for example, the charges they make for offshore services, or by charging tax on the companies based in these places.”
That is, these poor places do charge companies for being there. And if they didn’t then they would have even less of an economy than they do now. They’re richer by being those tax havens already, not poorer.