This might be an unpopular opinion, but any social program must be able to accept some level of "shrinkage" in the form of fraud. Just as retail businesses generally accept some level of loss to theft, return fraud, and shipping damage. Trying to create an "ungameable" system will either create a bloated bureaucracy that no one will want to use or will require a surveillance panopticon.

That's not to say that fraud should no be investigated and prosecuted. Just that it's important to accept that you will never get fraud to zero and there will always be that one guy who's collecting benefits for a bunch of made-up identities.

10% is not very much when it comes to barriers to UBI.

If you told somebody who supported UBI that it was going to cost $1.1*X rather than $X, would they stop supporting it? If you told somebody who opposed UBI that it was going to cost $0.91*X rather than $X, would they stop opposing it?

This is a good point. By widespread concern, I meant rather that tax return fraud generally does not rise to the level of campaign issue for people aspiring to political leadership.

I'm not actually sure whether refunds or total revenue is the appropriate denominator. The IRS collected about $3 trillion dollars in revenue, which would bring the rate down to 1 percent. On the one hand, refunds are linked to the total tax paid. On the other hand, there's other kinds of tax evasion, which would raise the fraud rate up again.

$30bil is not the correct numerator, regardless of if you take total tax revenue or refunds. The $6bil is.

That number also includes people who got scammed out of their tax refund by third-parties. Worldcoin would not prevent that; if anything Worldcoin looks exactly like one of those scams.