Why does Google use a blacklist of characters and not a whitelist? Only letters, numbers, punctuations in targeted languages should be allowed.

what makes you think that they don't do this?

> Any ad that contains a character from a predefined blacklist of special characters is automatically flagged for manual review and promptly denied by Google's approvals department.

I can understand the use of blacklist for flagging for manual review. But I don't understand why new, previously-unknown characters are allowed. If they were using whitelist for approved characters, certainly the emoji characters would have been stripped, replaced, or flagged for review.

Google will patch this quickly, AdWords integrity is critical to them.