We are obligated to respect the rights of other people, to uphold justice for everyone, but caring about people is something we (should, at least) choose to do because we recognize something deserving of caring in another person.
By whom? Why? If I was an athiest I wouldn't give a thought to any of that. I'd take what I want, when I want. That's assuming I believe 100% that there is no PURPOSE or creator-force (which I would never), or GOOD in the world (which can only be a product of a creator-force).
That's the basic idea of athiesm. Anything else implies a moral guide that PRESUPPOSES some sort of spiritual retribution for negative action.
If there is no spiritual retribution, then there is no reason to do good. Since "good" is just a manmade concept that doesn't matter if there is no creator-force.
I really wonder, you claim to have a purpose without a creator. That is the very definition of NOT having a purpose. To not have a creator-force, means you are but a RANDOM spawn without purpose from a universe that was "never created".