The right wing characterization is also cartoonish. It's on purpose. I could have said "extreme" instead of "pure" and perhaps you would not have objected.

As for lack of diversity, there are left wingers out there who'd agree with my characterization, so long as I'd give the mice blank/identical brains as newborns, but diverse physical characteristics. The idea is not that the mice stay the same forever. The idea is that left wingers tend to believe that we're all born with very blank and malleable brains, and that despite this, we become diverse as adults, because we grow up in different circumstances. For a left winger, this is a positive message, because it means that anyone can become anything if they just put their mind to it.

The right winger will tend to believe that "once a bad seed, always a bad seed", and will, for example, be in favor of death sentences, because he thinks it's not possible to change people. The left winger sees a prison sentence in a completely different light, as an opportunity for reform, because of his unwavering belief in people's ability to change for the better.