The presence of celebrities can draw criticism, but that is outweighed by the benefits. Some argue that pop stars only take part in charity to improve their public image. That, arguably, may be a motivation, but their participation can be essential to the event's success. Celebrities not only promote catalytic philanthropy, they can produce an effect some call "Geldofism": "The mobilization of pop stars and their fans behind a cause." Therefore, because of their visibility, celebrities are used by organizers as a mean to gain support to the cause in hand.