"We all copied off the same guy's test."
How did it come to pass that, as a basic tenet of Christianity, we are supposed to love our neighbors as we love ourselves? And those who follow the Muslim faith are to pardon and forgive others, for Allah loves those who do good to others? All major religions that people adhere to en masse have the same message, because it's a good one: do good, be good, and everything is good. Only an idiot would argue with that, right? This is the point where you ignore our history of religious intolerance and bigotry and agree that, fundamentally, every human who is "normal" believes the same thing. Theists, atheists, and agnostics likely all believe or will pay lip service to the ideal that we should treat each other as we want to be treated. We should be nice and not harm or steal from one another. In fact, I will argue that you can't reasonably, rationally propose another method of existence. No sane person could do so with sincerity, because to propose a world in which it is OK to harm some, to kill some, to steal from some, is to readily accept that you are OK with being harmed and killed yourself, for any arbitrary reason, and I believe no one who is rational would ever accept that. So it's wrong.
It's a reasonable argument to make that we believe goodness is not a construct of man. Goodness and the idea of what it means to be good exist independent of man (even of God, whether you believe in it or not). Goodness and rightness exist independent of us and are things we aspire to, and that's why all religions, throughout all time, have included these things. It's no accident or crazy coincidence. So a major aspect of simply existing is doing good. Being good. And by this definition, it's a pretty passive thing. It doesn't take a lot of effort. Not harming someone else is as simple as staying in bed instead of stabbing your mailman. Not stabbing the mailman is a good thing. You did well today.
"I enjoy not being stabbed! Thanks!"
I don't want to make anyone think I'm suggesting that the meaning of life is to be found in religion. Religion, I would argue, is a good place to start looking, because it tries to answer those tough questions of how and why things are, and it's how people have organized themselves for a hell of a long time. It's like learning sex tips from an elderly person -- they have the history to back them up, even if the reality of their involvement in it is horrifying.