Many people categorize rats as filthy and scary. In fact, many stories blame rats for carry disease and being responsible for the Bubonic Plague. Rats have a bad image. Many people have discovered that rats make excellent pets and are a good pet for children. Rats are rodents and belong to the same family as mice.
Many people think about calling the exterminator when they see either.
It is true that wild rats can carry disease and it may be entirely possible that they contributed on some level to the spread of the Bubonic Plague. One has to keep in mind though that all wild animals can carry and spread disease. Humans have nothing to fear by the domesticated rats that are sold in pet stores. Rats are generally very people-oriented. They are extremely friendly and tolerate many hands-on encounters.