I don't think steemit is going to fail because of copy-pasting prohibition, it allowance will, you see, the whole system is based on hard (or not so hard) work of authors and commenters, now imagine everyone can get easy steems by just visiting news and copying it, given that, it's matter of time steem as a currency is to fail.

Every cryptocurrency network gives rewards, i.e. bitcoin network gives reward once node proved it did useful work and created longest blockchain, this is done by consuming CPU/GPU/ASIC power. But Steem's core concept is that same mechanism is done by the user considering he did some work i.e. posted content, upvoted post/comment, or participated in mining. And copy-pasting content from other resources is going to kill that mechanism

This is how I see the problem with duplicating content from other resources, but I neved dived in, if I'm wrong at some point, I'd be glad to hear points.