Answer from "Marsh Maven", a Marine Biologist:
That is a hard question to answer. There are many reasons why people treat others badly. Sometimes it is as simple as the fact that people let it happen. Many times, though, it is about fear and power. When people fear others because of their gender, nationality, etc., they tend to treat them badly because they use their fear as a guide. Often fear is brought on by ignorance of other people and once people are educated about others' differences, the fear goes away. Sometimes it is the same principle as the school bully, that person is empowered by putting someone else down, and the actions are brought about by a need to have power over someone else. Naturally, if you are the person treated badly, it tends to make you think less of yourself. When I am in that situation, I always think of the words of Eleanor Rooselvelt, "No one can make you feel inferior without your consent."

Answer from "vet_in_04", a Veterinary Student:
Some people out there still think they're living in a time when women weren't allowed to vote or even speak for themselves. It takes a lot of time and patience to get past all those prejudices, but women are proving more and more everyday that they are just as capable as men at whatever they set their minds to do.

Thanks to Christine from Healey Middle School for submitting this question!