What's also interesting is that Penn rails against the government a lot in the episode (Penn's obviously libertarian), but thankfully due to government regulations, landfills are well-engineered to be safe for the environment. And landfill safety is one of the points that Penn uses to refute one of recycling's benefits.

Also, they say that a square landfill that's 35 miles on a side could hold all of America's garbage for the next 1000 years. I know they're not serious about it, but realistically you cannot have a central place to hold all the garbage since you have to ship the garbage to that one place (thus wasting energy, manpower, etc). So we still have to make do with landfills all over America and the problems of finding places to put new landfills still exist.