Allelic degradation hypothesis

I've often been thinking about how people say that the redhead phenotype is going away. This is true in a lot of ways. However, the alleles in the genetic world pool are not going away. However, it could be said that the inability for a phenotype to be expressed in the real world means it's undergoing an allelic degradation. What I mean by this, is that the lack of phenotypic expression is tied to all the other genes in the person's genome. And all genes work together for the fitness of the individual. A gene that is not phenotypically expressed means that it has not been required for survival. As such, it undergoes degradation. It will disappear from the gene pool, because it is not required for increased fitness. Furthermore, individuals have no way of being selected for that phenotypic expression, since it's unknown whether or not it is there.