Oh, for God's sake. Someone's feeling cynical.
This is not how humans are portrayed in the SC2 universe, anyway. The human society of the future is much more peaceful and rational than the nations of today, and even at our worst we aren't as bad as many of the fictional races portrayed in the game. It shows as much lack of imagination to claim that human beings are the worst possible race in the universe as to claim they are the best.
And why does everyone pick on the last 2000 years? Human beings have been fighting for much longer than that. Is this some misguided attempt to blame Christianity in particular for the bad things of the world, or something?
It is not conclusively proven that Humans and Syreen are cross-fertile. The only things known for sure are that Zelnick is telling is telling the tale to his "grandchildren" at the end of the game, and that those grandchildren are not obvious Human/Syreen hybrids. There are several explanations for this:
- Humans and Syreen are cross-fertile; human pigmentation genes (melanin) are dominant and thus will not appear in offspring if a Syreen appears at only one point. Syreen are, for all practical purposes, another race of humans (but are not Humans -- this term reserved for the Earthlings).
- Humans and Syreen can breed, but the offspring are not fertile; these children look human because they are -- Zelnick and Talana's children adopted. Syreen are hominids, but not (small-h) human.
- Humans and Syreen cannot breed; Zelnick and Talana themselves adopted. Solves all these problems neatly.
- Humans and Syreen may or may not be able to breed. We don't know, because on Unzervalt, "Grandfather" is simply a term of respect for the aged. Unlikely at best.