A person can already copy external content to steemit if they are the creators of the content like @talanhorne.
Many like me will make comments, critiques, reviews, etc on external posts and include quotes and links to the post. Which is covered under "fair use". For example: https://steemit.com/marijuana/@patrice/sorry-hugo-colorado-there-s-no-marijuana-thc-in-the-water-afterall
What people are doing is copy/paste entire articles from external sites without adding anything anything of value, sometimes they don't even provide the source wanting people to believe that the article was their work.
Steemit is about rewarding community members for creating great content and rewarding community members for recognizing that content. Not to provide another platform to drive traffic and create revenue for external sites such as Coindesk, CNN, FOX, Facebook, etc
I don't think there is a good reason to allow users to simply submit links to external sites. Why upvote/reward someone for just submitting links to articles on external sites. Especially when you have 100 other people submitting the same links.