You’ve posted this further up as well, but it is simply not true. The whole point of copyright is that no-one can re-publish (‘copy’) a copyrighted work without permission. News sites pay for the right to republish Associated Press reports, for example, as ‘hueving’ points out.

Aggregators like Hacker News and Reddit don‘t copy content as a whole, they just provide links. Providing a preview of the content, as Facebook does, might be considered either fair use or citation—but in neither case they’re copying and republishing the entire content.

Attribution does not magically remove copyright.