Suppose we discovered that gay people have a tendency to be better at sport, and black people a tendency to be smarter. That white people have better reflexes, and asians can remember things really well. All the "discoveries" about physical attributes have a pretty good chance of being tolerated by society, all the ones about mental attributes are likely to cause a massive public outcry.
For the scientific/analytical thinkers, this taboo of researching certain things is a bit weird. There is essentially the potential for knowledge that we're not allowed to discover. The steps to gaining that knowledge can be perfectly ethical, but the knowledge itself is toxic.
This generally troubles me. This idea that I can't talk about certain things, even if it's just to try to get people to point out the flaws in my reasoning... It's like a kind of self-imposed censorship.