A segregationist is a person who believes in or supports the separation of different groups of people, especially based on race.
The word segregationist has a very negative feeling because it is connected to unfair treatment and discrimination.
Examples:
The segregationist wanted to keep the schools separate.
The segregationist thought that people should not mix.
The segregationist's ideas were not fair.
The segregationist's ideas are as old as dinosaurs.
The segregationist wanted to separate everyone, even families.
The segregationist's ideas are not nice.