I had a teacher in high school who would give a whole lecture every year about "the bars of the cage".
The general gist is that 90% of the people in this world do not see the bars of their cage. They do not want to be freed etc. You 10% out there DO, and more's the pity because there's a happiness-in-ignorance that will forever be denied to you because of it. And now, for the really screwed up part: YOU are responsible for the other 90%.
The phrasing and analogy is a bit clumsy with just what we're talking about with responsibility, but the truth is there's LOTS of different bars in society, and I can only see some of 'em, and I'm never going to get all the way through even one but I can pick one as my time and energy allows and file away best I can.
To answer the questions directly: Yes, I think once you see suffering or injustice, you have some responsibility to do something about it. It's just not even a choice to me: you can't unsee the bars of the cage, and I know I couldn't live with myself just pacing about inside the cage: I don't think one person can save the world, but perhaps he or she can save another person. Or a group of people. What fulfillment of that responsibility looks like is going to be different for everyone, and I think that's kind of the point because there's SO many different kinds of problems.