You have accidentally hit rhe nub of the matter. Sociobiology is hated because it raises questions asssociated with Nazism. But Nazism did not come from nowhere. It was a bastard child of Darwinism, because Darwinism was quickly appropriated by those looking for a scientific vehicle that could carry the notion that some human groups were naturally inferior to others.
In a society such as ours with a faith in egalitarianism, that is a dangerous notion, and for that reason sociobiology is unwelcome. It weighs heavily on the soul of anything who ascribes to the doctrine that all men are created equal.
Have you actually looked at the history? It wasn't all that quickly. Scientific racists confronted with Darwinism tended to cling to preceding paradigms for some time, and in many cases for some decades. Haeckel in Germany, who set about recasting all his views in a Darwinian guise as early as 1864, is the only notable exception I'm aware of.
Many scientific racists didn't even begin to react until after the publication of The Descent of Man in 1872, where Darwin first publicly broached the topic of human evolution. Even at this late date Darwin found the anthropological debate over whether human races were separate species a current issue that had to be dealt with in some detail.
This delay response was especially pronounced in America where the Civil War understandably diverted attention from the Darwinian debates, and scientific racism tended to be tied to the more extreme "polygenist" view, that races were not just separate species but separate creations.
But even Alfred Rosenberg who I mentioned before (the Nazis' most important philosopher of race) wrote in the late twenties of each race being "created" with it's own unique "race soul".
The early reaction to Darwin not uncommonly (especially in the popular press) included some shock and concern over it's perceived tendency undermine or eliminate generally accepted racial prejudices of the time. For instance in 1866 the Pall Mall Gazette complained of Darwin associates Huxley and Lyell that their views on the "development of species" had "influenced them in bestowing on the negro that sympathetic recognition which they are willing to extend even to the ape as 'a man and a brother'." (Darwin, Desmond & Moore, pgs 540-41.)
In fact I'd say it wasn't until the late teens of the 20th Century that there was a resurgence of scientific racism equal to that of the pre-Darwinian mid 19th Century. (This resurgence was, I think not accidentally, coincident with historically unprecedented waves of mass immigrations hitting Western Europe and America.)
Where are you getting this notion? Sociobiology is controversial, but not because it's racist.