Landfills are a huge source of environmental degradation - to all media, and incinerators are notorious for going 'off-license' with their emissions. Any large scale garbage collection and treatment, to be most efficient is going to require the same level of sorting as recycling - there's simply stuff that won't burn and stuff that won't biodegrade and stuff that is too hazardous to allow into the public trash stream.
Recycling stuff, depending on the methods can be a squeaky clean process in comparison to traditional trash disposal. It costs more because the processes are much more regulated. Traditional garbage disposal would cost as much if not more if landfills and incinerators had to meet the same level of environmental standards as reuse industries.