The actors and actresses who attended the Golden Globes decided to wear black because this is their way of showing protest about the sexual misconduct that has been occurring in Hollywood. A lot of them understand that there is an imbalance in Hollywood wherein those who are in power may take advantage of those who would like to enter the world of Hollywood.
This should be stopped as everyone deserves to be treated correctly no matter what their age, sex, or gender is. Their choice to wear black is also for those who have decided to come forward with the things that they have experienced in Hollywood. Their stories have helped raise awareness.