Well, I won't give you 20 facts, but I can give you one major reason why animal testing is a good idea.
Studies have shown that doing animal testing can be beneficial for finding links in diseases that occur in humans. Many times, rats or mice have been tested to see if they respond to medication used in humans to see if they may or may not contract certain diseases. The whole point is, diseases occur in humans and animals. By doing the tests, researchers can find out if animals have certain immunities that humans don't. As a result the researchers can fine tune the medications given to ensure that humans get treatment and it may provide the missing links into disease research and it could save countless lives.