You're joking, right? The overwhelming majority of sites either don't care or are positive towards stuff like Pinterest (more ad eyeballs, for example). It's the rarity to [i]not[/i] want to be shareable.
No, I'm not "joking". The default license for content without an explicit license is that it is copyrighted. There are existing tags for looser licensing (e.g. creative commons). This is an obnoxious demand, and the "we decide whether it benefits you, and thus determine how we violate your rights" is a garbage way to proceed. No kidding it serves pinterest, though.
A relatively tiny site is demanding a site-specific meta tag for them to not commercial benefit by violating your copyright. Google, in contrast, observes long existing, cross-industry tags and behaviors.
And Google is hardly the example counterpoint: Many of its activities do border on very questionable. In Google's ideal world you never leave Google.com as they're filtered everyone else's content down to everything you need.
Yup, I have. And saying "fair use" makes about as much sense as saying "abracadabra" -- it's an incredibly narrow set of criteria that you can use if you're actually in court, not a magic word you can utter to make things work to your advantage.
Meanwhile, the assumed default status of anything created in a Berne Convention country in the past 90 years or so is still "all rights reserved".