That's the one I understand least. I wouldn't feel guilty about recommending stories that have the share button disabled, because I don't think it's settled and I don' think anybody really agrees what the point is! I leave them out partly as an excess of caution and I think partly just because, I think of rec'ing as partly a nice thing being done for the author, and if they're going to be confusing about it and make it harder there's plenty of other stuff to rec, you know?