I don't have an opinion on whether the subject is a case of gene selection or gene expression, but your binary caricature of evolution is misleading. A trait can be weened from the gene pool simply because it costs energy without providing a benefit, causing those with that trait to underperform compared to those without it. Even if individuals are living and passing on their genes, a trait might fade from the gene pool over time because competitors are able to claim a bigger proportion of resources, reproducing quicker and more often.
The human appendix is like that: it isn't directly harmful, but it's shrunk simply because it's a waste of energy.