The question how to find meaning in life is a different question. But I already gave an answer with me hinting at Existentialism. (I personally don't believe in an universal meaning of life. I happen to exist, and so I have to do with what I got, and that's just me. This is pretty close to, but not the same as Existentialism.)
As I don't want those things happen to me, I don't do them to others, because I only can expect others not to do them to me, if they can be assured I don't do it to them. I don't need pre-existing values. I just have to accept everyone else to be like me.
(This is just the simple version. The more elaborate version of the rule is Kant's Categorical Imperative: "Act only according to that maxim whereby you can at the same time will that it should become a universal law." We could also go into Existentialism and postulate that personal freedom, individual responsibility, and deliberate choice are essential to the pursuit of self-discovery and the determination of life's meaning.)
You don't kill the poor and the sick, because you don't want to be killed if you get poor and sick. You tell the truth because you don't want to be lied to. You want to give people making bad decisions a chance of redemption, because you want the chance of redemption if you fail. No God needed.
I subscribe to H.L.Mencken's attitude though:
We must respect the other fellow's religion, but only in the sense and to the extent that we respect his theory that his wife is beautiful and his children smart.
That's why in the U.S. constitution, it is clearly stated that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; [...]", because of the horrors of Christian intolerance. That's why one of the central ideas of the Enlightenment was the Freedom of Religion, the freedom to chose whatever you want to believe in. Grudgingly, Christian communities agreed, but needed another 150 years to do so.
Religious tolerance is not a feature of modern Christianity. It only exists because of exterior forces.
He's like a function -- he returns a value, in the form of his opinion. It's up to you to cast it into a void or not. -- Phil Lapsley