Social generalizations do cause alot of problems. The idea of validating and perpetuating these kinds of generalizations seems like they could be damaging to someone, someday.
On the other hand, these social generalizations are but a subset example of how we make sense of the world.
In context of Piaget's cognitive development model, these capacities emerge at the concrete operational stage.
wiki said:
The Concrete operational stage is the third of four stages of cognitive development in Piaget's theory. This stage, which follows the Preoperational stage, occurs between the ages of 7 and 11 years and is characterized by the appropriate use of logic. Important processes during this stage are:
Seriation—the ability to sort objects in an order according to size, shape, or any other characteristic. For example, if given different-shaded objects they may make a color gradient.
Classification—the ability to name and identify sets of objects according to appearance, size or other characteristic, including the idea that one set of objects can include another.
http://en.wikipedia.org/wiki/Concrete_Operational#Concrete_operational_stage
In other words ranking and categorizing. The two taboos of a liberal arts education.

With good reason, categorizing people goes hand in hand with ranking them. When you subconsciously rank people in terms of value that's where problems arise. On the other hand, categorizing and ranking is what brings us some of the best in humanity. Categorizing the physical world, ranking what is ontologically primary, etc.... This capacity is essential! It's the same neutral technology being used for both good and not so good.
The characteristic problem with the concrete operational stage is...
wiki said:
Children in this stage can, however, only solve problems that apply to actual (concrete) objects or events, and not abstract concepts or hypothetical tasks.
People at concrete operational may see patterns associated with differentiable groups of people, but they lack the abstract thinking to see why this may hold true. I say this with a bias obviously, but such generalizations are going to be more partial than logically informed ones.
The next stage in Piaget's model
Formal operational stage
The formal operational period is the fourth and final of the periods of cognitive development in Piaget's theory. This stage, which follows the Concrete Operational stage, commences at around 12 years of age (puberty) and continues into adulthood. It is characterized by acquisition of the ability to think abstractly, reason logically and draw conclusions from the information available. During this stage the young adult is able to understand such things as love, "shades of gray", logical proofs, and values. Lucidly, biological factors may be traced to this stage as it occurs during puberty (the time at which another period of neural pruning occurs), marking the entry to adulthood in Physiology, cognition, moral judgement (Kohlberg), Psychosexual development (Freud), and psychosocial development (Erikson). Some two-thirds of people do not develop this form of reasoning fully enough that it becomes their normal mode for cognition, and so they remain, even as adults, concrete operational thinkers.
Interestingly there is a correlation between institutional/cultural structures and cognitive structures. The two go hand in hand nearly always. You'll find rational(formal-operational) people where the institutions of the Enlightenment are setup. People need a space, culture, and language to be rational before you can really start seeing it appear on meaningful scales. Similarly you'll find concrete-operational wherever you find mythical religious institutions. In the absents of either of these kinds of institutions you'll find syncretic magical thinking wherever you find tribal institutions.
The root of the problem isn't that we live in a world of generalizations. The problem is we as a society haven't yet done enough to get more people up to speed on critical thinking.
Part of the problem is institutional. We all know that traditional institutions can be very homogeneous, and wary of outsiders. Even if people are ready to pop out of the concrete-operational stage the structures of traditional institutions are designed to make it very difficult. Cultural isolation, being ostracized, etc... Living in some rural areas this unfolding may be outright dangerous to your well-being! Not surprisingly rural areas have higher centers of concrete-operational.
On the other hand, imagine being at the concrete operational stage and having all the mythical belief systems correlated with it. Well going to a university might be a very painful antagonizing experience for you. All the sudden things like values, morality, and God which gave you value in your native institution do no such thing here. Not only that but they actually de-value you in the eyes of your peers!
These institutions exist as fragmented islands at odds with one another. In the process of this all sorts of people are getting marginalized. The people that ironically need it most.