Whether or not adding some form of “Share” prompt to your content equals the relinquishing of copyright over that content is currently being hashed out in legal venues and is a situation that all publishers should be watching closely.
The thinking apparently goes like this: The key point made by those claiming copyright infringement around their content on the web is that people are viewing it elsewhere and not on the domain it originally appeared on. But adding some form of “Share” button inherently, it’s being argued, waives any copyright claims since the only purpose of having it there is for the off-domain sharing of content.
While I’m certainly not a legal expert in any way, the leap between someone who’s lifting a full story and putting it on their own site without a link to the original for the purposes of generating ad revenue and sharing a link to the original on Twitter seems to be a pretty massive one. That would, in my mind, mean that even providing a URL to a story would be enough to waive copyright since the purpose of a URL is to point someone to something specific and it can be easily put manually into a social network update or email. That’s a pretty broad argument and one that would have far-reaching implications on publishing across the entire web and not just in the media world.