So what's the actual proposition being asserted by "fitnessism"?
It looks to me as if the path to "fitnessism" goes like this: (1) Contemplate evolution. (2) Conclude that people (and other animals) act so as to maximize their genetic fitness (this is error #1, conflating adaptation execution with fitness maximization). (3) Conclude that "right" means something like "tending to maximize genetic fitness" (this is error #2, conflating ought with is).
Perhaps I'm missing something important; Survival Machine, would you care to set me straight?
None of your propositions reflect any claims made by ethical fitnessism.
Ethical fitnessism is a normal moral theory just as hedonistic utilitarianism, but with differences in its meta-ethics and intrinsic value. It violates neither Hume’s law nor the naturalistic fallacy. It is not the case that nature or evolution implies that ethical fitnessism is right in any higher meaning.
Fitnessism has no special naturalistic definition of the word 'should'. It uses 'should' in the same sense as utilitarianism does.
For a further description and explanation of fitnessism please see my response to DeVliegendeHollander.
I noticed that there has been some earlier discussion about Sam Harris’s Moral Landscape Challenge here at LW. As a writer on the Swedish politico-philosophical blog The Inverted Fable of Reality, I would like to share a response to the challenge, written by our main contributor, which I believe is interesting to read even if you are not familiar with The Moral Landscape or its content. See this link for the response and a short explanation of the challenge.
The response takes a different approach to most responses to the challenge. It is divided into four parts and starts by asking which ethic is most compatible with science and reality and finally tries to answer this question.