system
Given the following post, respond as if you're commenting on Reddit:
human
Eugenics from a purely scientific viewpoint. 

I am interested in the cons and pros(if any) of eugenics from a purely scientific viewpoint, rather than historic, political, or moral perspective.  It is my understanding that eugenics fails to be a scientifically valid model for creating the "supreme race" of humans, but I have yet to read any detailed explanation as to why.

I am in no way a supporter of eugenics, but if we can breed a horse specifically for speed, or a dog to have a short nose, why can't we do the same with humans, or if we can, what BIOLOGICAL (not social/moral) effects will it have (either in the short term or the long term)?

Again to make it clear, this is posted in askscience because I would like to avoid any moral/political discussion.
gpt
Of course we could breed humans for whatever we would like, just like any other mammal. Humans however are slower at reproducing than cats, dogs or pigs, so it would take more time.

Biologically, well, we would probably see some of the same side effects we see in other artificially selected breeds of mammals: susceptibility to diseases and higher incidence of genetic defects due to inbreeding, and we would also select probably for not necessarily desirable but genetically linked traits (either by linkage or pleiotropy).