Mike makes it clear why he thinks everyone wouldn't add the flag: If Google comes across a large website that has a tonne of "original source" content which lo

Mike makes it clear why he thinks everyone wouldn't add the flag: If Google comes across a large website that has a tonne of "original source" content which lots of other sites are claiming "original source" for, then they can automatically identify it as a scraper site and penalise/flag for manual checking. (I disagree with him that this would work, but that's clearly his line of reasoning. The most obvious failure mode is if a site mirrors all of SO's content, but nothing else, and puts the flag on it, in which case the flag doesn't help you distinguish which site is the source.)