All kidding aside, go look at how much energy is required to manufacture and transport paper bags. Everything from pulpwood harvesting and transport to paper production, bag production then shipping. It takes a lot more resources to produce and utilize them than plastic, however... people don't dispose of them properly and...

http://www.treehugger.com/culture/paper-bags-or-plastic-bags-everything-you-need-to-know/page5.html