I think rat meat is perfectly edible. Some of my relatives claimed they ate such before. They have been television stories in which the topic is a man who love eating rats. My cat and the previous cats I had were hunting and eating rats. No reports of rat poisoning so far or studies about its potential toxicity.
However, eating rat meat is a no no for many. The organism is seen as notorious pest, eating precious amount of crops. A dirty animal, living on dirty canals and garbage areas. A deadly disease vector, a leptospirosis disease causing bacteria is living on its digestive tract. The disease is manifested once the bacteria entered human blood stream thru wound opening.
If adding horse meat to burger patties is disturbing. Then what about knowing that some enterprising individual are slaughtering rats and selling it as lamb meat? You may never want to buy another kilo of lamb meat again.
Recently, 63 people were captured (by Chinese authority) and found involved in slaughter of rats, minks, foxes. The meats were added with gelatin, nitrates and pigments to mimic the lamb meat appearance and sold it as such. The meat group has not been tested for quality and safety. Added the fact, they are fooling the customers into believing it as lamb.