As I have stated before, this is a problem I have for a lot of the "research" that supposedly finds evolutionary "adaptive" reasons for human beauty.
1) Standards of beauty are so culture specific, and even within a given culture are affected by fads and temporary fashions, that researchers should have to realize they need to work a little harder to even establish that there is some sort of innate standards of beauty.
2) Even if there are innate standards of beauty, they could, as you point out, be the "unintentional" result of brain processes that were selected for other reasons.
3) Finally, even if certain standards of beauty were selected for, it could be the result of sexual selection that has nothing whatsoever to do with any kind of fitness of the individuals.
A lot of the pop evopsych that I see in the mainstream media seem just like the "just so" stories that the creationists complain about.
"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt