Please elaborate why is it not "scientifically sound"
You concluded, " It's the desire to stick out from the crowd, to be different."
If you take someone with Epidermodysplasia verruciformis, they are very different and 'stick out from the crowd', only 4 recorded cases in medical history. So by your conclusion, everyone would want to look like that. I don't have any physical evidence from a survey or such, however, I would tentatively say that a statistically significant number of people would not want to look like that.
features and traits associated with 'beauty' tend to be traits that genetically dominate.
If you associate a skin rash with beauty, one could argue the thing that causes you to make that association in itself is a genetic deficiency.
If that genetic deficiency causes you to procreate with someone having some sort of skin disorder and your children end up with a disease that causes their death before puberty, it is a clear case of natural selection.
All genetic changes are designed to suit their environment, and genetically superior individuals should be able to identify others with superior genetic traits and associate them with 'beauty'.
I don't find red heads or freckles attractive because of the environment I am in and rightly so, red-haired individuals are associated with type 3 albinism.
Red heads are caused by genetic mutation of MC1R protein, it only is caused when two recessive red haired genes are in existence.
In the same way, if we dig a little deeper into a 'normal' individuals desire, we are likely to find some sort of advantage that would lead his children out competing for other children of the same species to adulthood.