When we dehuminize another person, it makes it easier to attack them. Since you have lowered this other person below human status, you have created an illusory situation in which is it justified to marginalize that person.
Whichever side of the political spectrum you fall, we are all guilty of this. How often do we begin a diatribe with something like “he/she is such a piece of sh**/b**ch” followed by some marginalizing characteristics that have been justified because of that dehuminzation?
What if we instead had to begin with the fact that this person we were going to dehuminize is indeed a human: a person just like you and me? Let’s start with that instead, and see where we go from there.