The Fatal Injury Rate in the US is %0.0192 or about 2/1000

0.2%, actually, which still sounds like a fairly low rate at first, but what is a good rate? These are not broken legs, but “injuries that result in fatality within 72 hours from the race date.” In absolute terms, over 700 horses were killed in races per year (1,532,418 starts × 0.00192 / 4 years).

If we disregard the reasons against comparing horses to humans, that rate corresponds to about a thousand deaths a year among marathon runners (based on 541,000 marathon finishers in 2013). The actual marathon death rate is about 3 per year, less than one per 100,000. And, of course, the marathon runners signed up voluntarily and had the option of dropping out.

If a two Olympic runners voluntarily had a child for purely genetic reasons, would that be bad?

One of my favorite couples is Dana and Emil Zátopek. They were both born on September 19, 1922. She “won a gold medal in the javelin throw at the 1952 Olympics, only a few moments after Emil's victory in the 5 km run.” Emil claimed his victory inspired hers, to which she replied “Really? Okay, go inspire some other girl and see if she throws a javelin fifty metres!”

They had no children, but I would be only pleased if they had kids hoping to produce a super-athlete. Partly because parents have surprisingly little influence over the course of their kids' lives, but mainly because the kid would presumably be free to pursue athletics or not.

It would be disconcerting, to say the least, if outsiders arranged couplings and controlled individuals in order to breed athletic skill.

No objections to your other comments. My opinion on horse intelligence is based on Cormac McCarthy novels.

Your summary paragraph hints at a dream scenario for animal welfare activists: putting sentient animals in the same category as children — creatures that deserve our special concern and compassion because they are vulnerable and dependent. There is a world of difference now in that we hope to intervene and protect children for their own good; our primary objective for animals is to meet human needs, with animal welfare a distant second.