"Humane or not, what is so especially "undignified" about rats? What makes them worse, than, for example, cats, deer or wild horses?"
The author of the summary has obviously never had a rat infestation. They can swim, dig several feet down, chew through concrete, plastic, wood, drywall, and otherwise go to amazing destructive measures to get to a heat or food source. Unlike mice, keeping your food in the cupboard or Tupperware containers is useless as they chew right through them, and destroy your home's foundation while they are at it. No, rats are not at all like wild horses, cats, or deer. Rats are a special kind of hell.
If you need an ecological reason. The destructive urban rats are an invasive species, not native to North America. We brought them here - and I for one applaud every effort to get rid of them.