Eugenics involves human beings making decisions, often ideologically motivated, about who lives and who dies. Natural selection is dispassionate and plays no favorites. In any case, I don't think the article defends eugenics; it simply claims that genetic decay is inevitable. In a way, it echoes the concerns raised by the theory of genome entropy, which is a controversial concept derided by mainstream geneticists -- partly because the proponent, John Sanford, rejects evolution. Personally, even though I accept evolution, I find the geneticists' rebuttals shallow and believe important questions are glossed over about the proposed mechanisms for evolution.
In any case, here's one way to view human civilization:
A biological organism is a collection of cooperating organs, where each organ is composed of highly specialized cells. The body's biochemistry is the glue that keeps the organs connected and functioning properly. For the organism as a whole to survive, even defective or injured organs/cells must be repaired or, worse case, carried as dead weight. The unit of propagation is the gene bundle comprising that particular individual.
A human civilization is a collection of cooperating individuals performing specialized roles. Culture, including morality, is the glue that keeps the individuals connected and functioning properly. For society as a whole to survive, even defective or injured individuals must be carried along. The unit of propagation is the gene pool of the society as a whole.