Fitness treated as a property of phenotype (or even of genes) rather than as a property of phenotype and environment.
I'm not sure what you mean. Do you mean that there are conditions under which being sexually attracted to members of the same sex is evolutionarily advantageous?
Or do you mean that the genetic trait that manifests as homosexuality, manifests as another, advantageous, trait under some circumstances? If so, this seems like a version of Darreact's "imprinting" theory.
I read an extract of (Wimsatt 1980) [1] which includes a list of common biases in reductionist research. I suppose most of us are reductionists most of the time, so these may be worth looking at.
This is not an attack on reductionism! If you think reductionism is too sacred for such treatment, you've got a bigger problem than anything on this list.
Here's Wimsatt's list, with some additions from the parts of his 2007 book Re-engineering Philosophy for Limited Beings that I can see on Google books. His lists often lack specific examples, so I came up with my own examples and inserted them in [brackets].
[1]. William Wimsatt (1980). Reductionist research strategies and their biases in the units of selection controversy. In T. Nickles, ed., Scientific Discovery: Case Studies, Dordrecht: Reidel, p. 213-259.
[2]. R. Levins (1966). The strategy of model building in population biology. American Scientist, 54:421-431.
[3]. Rudolf Raff (1996). The Shape of Life: Genes, Development, and the Evolution of Animal Form. Chicago: U of Chicago Press.
[4]. They let you use multiple GO tags, and put multiple names within a protein's name field if separated by slashes, but these are not adequate solutions.