We would evolve to be attracted to objects or actions that promote evolutionary success, regardless of their 'intended' (by who?) moral status. Moral properties would be just another bit of data (alongside photons and soundwaves) for us to work with and interpret for evolutionary ends. Again, there's no reason at all to think that we would learn to distinguish which properties were intended to mean 'good' and which 'bad'. If intrinsically 'bad' things increased our evolutionary fitness, then we would come to (mistakenly) interpret them as 'good'.
So unless one wants to conflate 'good for my genes' with 'morally good' (not a good idea!), we must deny that objective moral properties exist independently, 'out there' in the world, waiting to be perceived by humans.
To which Brandon of Siris made the interesting response:
But suppose someone were to substitute 'perceived properties' for 'moral properties' and modify everything else accordingly? The conclusion would be that, while there are real facts of the matter, and while our cognitive functions are such as to promote evolutionary success, we have no reason to think our cognitive abilities map the world.
But note that I never suggested we wouldn't be able to accurately perceive (the existence of) moral properties. Perceiving them would be a prerequisite for our being able to use them as information for evolutionary ends. Rather, what we must be blind to is their 'intended' status.
Evolution implies that we should be skilled at perceiving various 'descriptive' properties out there in the world, but utterly blind to any normative ones. Or, to put it another way, we should have fairly reliable 'existence detectors', capable of distinguishing various physical phenomena, but any deeper 'meanings' should be inaccessible to us (at least by direct observation). If there were intrinsic moral properties out there, we might detect their existence (being a descriptive aspect), but not their goodness (the normative/'meaningful' aspect). We instead 'attach' the normative attitudes ourselves, having developed pro-attitudes towards objects that improve our evolutionary fitness, and con-attitudes towards predictors of evolutionary harm. (Thus the relevance of evolution to aesthetics - why we love a lush countryside but are repulsed by mould and faeces.)
What Brandon calls our 'perceived properties' (I assume he means things like colour, shape, distance, etc.) don't have any 'intended' normative status. (Or if they do, then we can't directly perceive it). But we should be able to detect the purely descriptive aspects of these properties just fine, according to my argument. So I don't think there's a slippery slope to skepticism here after all.
Perhaps Brandon is pointing out that what we see must not be what things "really" look like. (Qualia would seem to be a deeper 'meaning', rather like normativity.) To which I would entirely agree - the universe doesn't have any mind-independent visual properties. It doesn't intrinsically "look" like anything. But we can detect the existence of various wavelengths of light, and then interpret this in an evolutionarily beneficial way - giving us the appearance of colours (for example).
So yes, my argument implies that our qualia will not map to the objective reality - the way things ought to seem (look/taste/smell etc). But that's okay, because there is no "way things ought to seem". There's just the way things are - the detection of which is surely in our evolutionary interests.