i think art, artists and operators, like all other persons, have a responsibility of the possibility for change. Anything we do in our lives has that responsibility, therefore, i do believe we should and have to think of our presence in the world as what it means in terms of change (change here being personal, collective locally and globally).
As for why art has that responsibility, well, when one has access to a public platform regardless of how small, she has a responsibility for using it. i do not think that one enters that space knowing of the change she will cause, but she does. The change is often small, but that is how most sustainable change happens.
Art perhaps has more responsibility for change than other disciplines because it can present new unthought-of possibilities, like a mathematical equation. It offers unique solutions and perspectives. Therefore, i think it is one essential tool in creating an alternative world to the one we live in now.