Chitra, if you really want to help someone, you should not think whether that would affect someone else. I am not going into the content of your thread because I feel that the title implies much more.
You must be able to select and accord priority when you decide to help someone; you will have to see whether the affect on another would be graver than the help you are offering to a person. I would like to agree with Aditya that thinking about the aftermath would ruin the essence of help. You may help a person and at the same time ensure that such an action does not affect another person negatively. You will have to weigh the pros and cons and decide which is more important.
Take an accident site for instance and imagine that two bikes have collided and you have injured persons before you. If you think that there will be a police case and that the person who has violated traffic rules may be punished, you may not be able to help a person to survive. In that case your priority should be to save a life and also to bring the wrong doer to books as law demands, at a later stage if required. I have cited a small example but the same benchmark applies in all cases where you intend to help someone.
Provide help to the one who need it most, the other side can be looked into later. Coming to your thread, while I appreciate the gesture of those who fed the cats, and do admit that it is the duty of the boy to keep the premises clean, I must say that it is more of a matter of civic and common sense, as Dr Rao has pointed out, and does not have much to do with helping others.
'It is the mark of an educated mind to be able to entertain a thought without accepting it'. - Aristotle.