I’d say that using donation matching without making it counterfactual is much more manipulative, because without establishing causality, you’d essentially be deceiving potential ‘matchers’. My proposal precisely aims to remove this deceptive potential.
It’s possible that this kind of donation matching essentially shifts power to large funders. I think this could be mitigated by having a long whitelist of effective charities (rather than one specific charity chosen by the funder), which gives matchers more leeway.
I think you’re probably right. The possibility of the funder being their own matcher-of-last-resort probably destroys the scheme. I hadn’t thought about this before, thanks for pointing it out.
One potential way to fix this would be to require the identification of donors, so that you cannot fund anonymously. But this would make the proposal a bit more complicated.