True, you and I are probably not basing our judgements on the same sample. I understand that many Black Americans are really bad, both in terms of intellect and in terms of righteousness.
I don't think you really do understand. It's not all individual people, but there is a very bad culture associated with them and if they don't follow it, they're seen as an uncle Tom, a race traitor, etc. by their own people. A successful, hard working, intelligent black can be made fun of as "trying to be white". It's true not everyone in that group is bad, but there are a very large number and very large percentage. So while I wouldn't be mean to anyone I didn't know, I wouldn't knowingly walk into one of their neighborhoods alone either.
But there are also a number of decent Black people around the world who don't deserve to be treated with such contempt. I have even known Black people who were quite brilliant.
In any population of people, there are going to be some that are brilliant due to a natural distribution curve. However the numbers for blacks as a whole do tend to be smaller than for other populations. A lot of African countries have extremely low average IQs and those with better nutrition and education in the developed world still tend to rank lower on average than whites and Asians. This isn't anybody's fault but it is a part of nature that nobody can change.
I've discussed this issue before : it's quite meaningless to talk about "Blacks" in general, they don't make up a homogeneous and consistent human subset, there are very different groups of individuals who happen to have a black skin and some African genes; some of them are educated, others are not; some of them are honest and hard-working, others are not. In this respect, it is not only very offensive but silly to talk about "Blacks" in general as a bunch of sub-monkeys.
Most blacks in the USA came from about the same area of Africa, and while they're not completely homogeneous they do have a lot of traits in common. In particular their culture ties different blacks together making them degenerate.