I think it is difficult to convince people of much, and feel it is a waste of time in most instances regardless of topic.
With that said. . .
Real-life examples help with this, but aren't as wide spread right now to make viewing easy in many instances
But . . . if you want to read up on the topic:
Mark Shepard lays out an excellent (seemingly, as thorough as possible) calorific comparison of industrial ag and restorative ag using his own farm as an example and using fairly conservative yield estimates where "hard" data is lacking/limited/developing.
His book is
Restoration Agriculture: Real world permaculture for farmers
I have heard Mark Shephard and also Patrick Whitefield ( I am sure others too) turn that question on it's head and ask: Can industrial ag feed the world?
Lots of starving people across the globe, and where bountiful harvests occur, much of it is low quality dent corn, gmo soybeans etc. -- so not really food and/or needs heaps of processing to become edible.
Degradation is prolific b/c of poor ag pracices (see dustbowl and up until today).
While I'm not trying to drive traffic away from this site.
PRI Australia just the other day put out a bunch of links and a video addressing this topic
http://permaculturenews.org/2013/01/07/food-mythbusters-do-we-really-need-industrial-agriculture-to-feed-the-world/
The video addresses the topic well, but rather simplistically imo.
Restoration Agriculture: Real world permaculture for farmers would be a good book you might both read and have discussions about.
I highly recommend it as a good read for anyone interested in this type of stuff, I even wrote a
goofy review of it here on this site.
acresusa sells it.
Have Fun!