Does a celeb help a cause?

Many bollywood celebrities have taken up social responsibility to the next level; today they not only lend their name for a cause but are also active participants towards the cause. The debate here is that many celebrities, especially bollywood stars have often been accused of using causes for publicity.
For example, Aamir Khan an ace actor is supporting the victims of the Bhopal Gas tragedy and the Narmada Bachao Andolan (NBA) the organization is a coalition of human and environmental rights activists leading a campaign to prevent a height increase of the Sardar Sarovar Dam on the Narmada River, for fears it would displace a significant number of villagers in Gujarat.
However, the actor received a lot of aggravation from certain political groups and activists. The Gujarat government banned Aamir Khan’s latest release Faana not because of the content, but because of his presence in the movie, as he is supporting the NBA. The controversy arose when media speculated that he was doing this to promote his latest film Faana, while the actor continues to endorse Coca-Cola even though Coca-Cola bottling plants in India received a lot of criticism for draining water, which took away the water supply of some villages. Many in India accused Aamir Khan of joining NBA as a public relations stunt to boost Fanaa after the mediocre box-office performances of his most recent productions. Whatever the reason, Faana did receive a fair amount of hype and media coverage over its ban in Gujarat. Later after sometime when the movie released in Gujarat people were flocking even more so to watch the film, even though it was just another Bollywood love story.
Sometimes it is hard to gauge what is a PR stunt and what is not, Aamir Khan has always been a part of many social service projects even in the past, and has never used any social cause to promote any of his films. On quizzing trade analyst Taran Adarsh he says that “for some celebes, it’s a mere gimmick to generate fan following and so, business for an upcoming movie.” But he quickly adds that “someone like Aamir Khan, who usually keeps away from the lime light, wouldn’t lend his name to a cause unless he feels very strongly about it.” However in a PR driven world one may just never know… do u think famous celebrities who need no more fame would adopt a social cause as a PR stunt to promote their latest release?