Objectivism

May be I am showing my ignorance, however, I have a question for objectivists. Why do people have a right to liberty? If existance just exists, how can you manufacture right and wrong? If I am an indevidual, why not just do the best for my self, sure be nice to people for my own benifit, but what does it matter if I hurt another person? If another person feels pain what does that matter? what is the difference between a person feeling pain and an animal (that supposedly has no rights) feeling pain? why should we care?

Now I dont feel this way, I believe in being kind to one another etc. But why do objectivists feel that in the world there is a "God Given" (even though they dont believe in god) set of rights that some have(born people) and others (Animals, foetuses) dont have? Why with an indevidualistic attitude does it do them any good to pedal this stuff when the're never going to get their way? Why when some libertarains dont even care if animals suffer pain, care whether the guy down the street should be allowed to take heroin for example?

I understand liberal values, but I dont understand this sort of absolutism, how can atheists have such absolutism? I believe that a foetus is person, however does it really matter if it is aborted.
As I have stated I dont particularly approve of abortion but I dont see it as an outrage like murder, but if I were libertarian I should because I believe it is a person.

To explain why I feel that a foetus is a person and not part of the mother, geography or location does not define indeviduals. Biologist would be outraged if you said that a lichen was one organism (although the initialy were classified that way). They would be horrified If you said that a parasite the same organism. Thats like saying that a protein from an E. coli, is not an E. coli protein, but a human protein from the E. coli cells.