Because in the movie, while (not necessarily spoilers) Finn, (token black guy. Great character) is running across a battlefield of an invasion on the soil he stands upon, a grim battle turns into a "what the **** that's awesome" battle when traitor trooper shows up.

Traitor trooper then proceeds to beat Finn (traitor of the glorious first order, rebel scum) into a proper pulp.

You find out Finn is a traitor when you meet him. So like I said, only spoiler I guess with what you asked for.

he was a better fighter than mr emo now that i think about it