>around 60% of rich-world respondents say they would be willing to give up 0.5% of their income if that were enough to end extreme poverty.
If they really were, they already be doing it, and it would be a solved issue. For many folks, it's a lot easier to say 'yes' to a survey about whether you would give your own money to the poor than it is to actually give your own money the poor.
When it happens collectively e.g. through taxes, you get somewhat of a middle ground between the survey and giving your own money (directly and visibly).
There seems to be some kind of international target of 0.7% of GNI (~GDP) for developmental aid already, which governments often don't meet fully but come close to (e.g. https://commonslibrary.parliament.uk/research-briefings/sn03...), so the 0.5% would probably be viable in tax form.
If they really were, they already be doing it, and it would be a solved issue. For many folks, it's a lot easier to say 'yes' to a survey about whether you would give your own money to the poor than it is to actually give your own money the poor.