Sustainable intensive farming gets more output on less land with less harm to the environment overall. Sustainable farming without the intensive part uses more land, which is bad. More land for agriculture means less land for grasslands, wetlands, and forests. Looking at the Big Picture, "sparing" the wild things is better than "sharing" with them. Of course, there will always be exceptions, but that's the general rule.
Sustainable intensification of agriculture doesn't mean you slather the landscape with pesticides and fertilizer. It means getting really good at precision application of pesticides and fertilizer to minimize externalities. Keep them out of the water and surrounding areas. And cutting back on pesticides and fertilizers while maintaining or improving yield. GMOs play a role here, but only a role. There's no one fix or approach.
Large farms in developed countries will lead the way because they have the resources to invest in and fine-tune the technology. Then we'd better make sure mechanisms are in place to help the rest of the world's farmers adopt whatever works. Share the technology if necessary.
References:
Garnett, T., M. C. Appleby, et al. (2013). "Sustainable Intensification in Agriculture: Premises and Policies." Science 341(6141): 33-34.
Tilman, D., C. Balzer, J. Hill, and B.L. Befort. 2011. "Global food demand and the sustainable intensification of agriculture." Proceedings of the National Academy of Sciences. 50: 20260-20264. http://www.pnas.org/content/108/50/20260