Why are mice in cartoons (almost) always depicted as good guys?

Question

Mice are pests destroying human crops. They have been hunted without mercy for hundred of years. Humans domesticated cats to keep them away from their houses and granaries. Poisons and traps were used extensively.

Yet in cartoons mice are almost always portrayed in a positive light, as opposed to cats that are very often antagonistic and villainous. We have Mickey Mouse, Minnie Mouse, Pixie and Dixie, Jerry from Tom and Jerry, Speedy Gonzales (and Slowpoke Rodriguez), An American Tail, Biker Mice from Mars, Mighty Mouse, Danger Mouse, The Rescuers, The Great Mouse Detective to name only a few popular titles and characters. The only show to have mouse as a bad guy and cat as a good guy I can think of is really obscure Klondike Kat (and maybe Simpsons' Itchy and Scratchy, but that's a parody). Pinky and the Brain are kind of in a gray area - they want a world's domination but again aren't actually evil or despicable.

Is there any reason these rodents are depicted as good guys this often?

Answer 1

It's just a working trope Nice Mice, unlike Rats, mice are smaller and do work as underdog character as other answer tried to say:

Very small and cute, yet wild, the mouse is an animal often used as a metaphor for someone easily underestimated. Thus, mouse characters and humanoid mouse races tend to be heroic and really good people, yet easily underestimated. In many works, this last trait is something they have grown to resent deeply. It's hard to demand respect from someone when you can't even reach his knees and your voice is very squeaky — no matter how brave you are.

On the other hand, Rats are mostly evil, refer You Dirty Rat! trope.

Answer 2

Isn't it as simple as predator/prey? In general, we cheer for the underdog and dislike the attacker.