If you cannot think abstractly, you see people as single entities and not a complex collection of different qualities and attributes.

They are a simple blob in their heads.

This allows bigots and racists to project faulty characteristics to groups of these "blobs".

When you can think abstractly you can build the different parts that are inside that blob. These include:
- Past experiences
- Family and community support
- Economics
- Role models
- Health

These, and more, make the person.