You're not talking about a 'meaning' for life here, you're talking about having a purpose.
Two distinct, but very closely related things.
Also, consider this: There may not be any purpose or meaning to life. And yet, it may nevertheless still be your responsibility to act with restraint, and treat each human being with dignity.
Even if the universe is cold and uncaring, we still have a duty to each other, and we don't need some magical 'meaning' to life to know that we have a duty to each other.