OK let's say there is no god and no afterlife. One person's morality is as valid and true as anothers. One person's view of human value or the lack of it is as valid as anothers. I will therefore live for my own self-interest and pleasure and achieve this at the expense of others if necessary. I will view humans as a parasite infestation responsible for the extermination of thousands of species (not that it matters) and I will work actively toward the extermination of humans, as the noblest moral obligation of a rational human being. Returning the earth to a primal state would level the playing field for ALL species. Thank you Smith and Dawkins for your valuable contriubtions to the final destruction of humankind. As Voltaire rightly said, "If there were no god, we would have to invent one." The question is not only one of the existence of god but also of the necessity of god, of a transcendent authority or standard without which there is NO standard of morality and NO human value.
You make the assumption that without gods, there is no morality. But there is no necessary logical connection there. God is merely an invention to explain what we don't understand. God was once used to explain natural disasters, both physical and mental illnesses, and just about everything else that was ever unknown. Why is morality any different? Since when are believers in some deity more "moral" than non-believers? And whose belief system, of the thousands from the past, present, and future, is the right one?
I have heard a number of people claim that there is no morality without a god. But I have never heard a plausible attempt at proof of that assertion. In fact, I've never heard any attempt at all. At most someone might say that it's "obvious," or "common sense," and so on. But if so then the proof should be just as obvious. So where is it?
There is simply no objective morality, no objective meaning, and no objective value, if there is no transcendent source. For example, why not exterminate humans as a parasite infestation of earth? This would be the noblest. We only know what is right by hearing god. So we can speak of the necessity of a transcendent source as evidence of a transcendent source. Without this, one persons view of right and wrong is as valid as any others. Without a transcendent source or standard, there is no way to place greater value or ANY value on human life above other life and non-life forms.
It is possible for there to be objective morality without a transcendent source. (Indeed, one might reasonably ask how a transcendent anything helps objective reality). It is, for example, an objective truth that the three corners of a triangle add up to 180 degrees, regardless of each individual corner's angle. This truth is objective entirely independent of God or human beings.
Now all we have to do is define morality as "a survival strategy for a social, self-aware species." Some survival strategies will clearly be more effective than others. We can say those are objectively superior. And there you go: an objective basis for judging moral codes.
What you think is right and wrong is what you evolved to think, just as what you think tastes good and does not taste good is what you evolved to think. Each of us has slightly different takes, and some of us have very different takes, but there's no particular difficulty in asserting that sugar tastes better than sawdust, at least to the vast majority of normal functioning human beings. This is in no small part because your tongue evolved receptors to taste sugar, and did not evolve receptors to taste sawdust, because eating sugar helps you survive and eating sawdust does not. In exactly the same way, morality - which really boils down to the concept of fairness - evolved because being fair (or at least being perceived as fair) helps you survive when you live in a social society.
It's not really that difficult. And it's not really without hope. Indeed, the metaphysical naturalist's view of morality is more hopeful than religion, because it argues that what feels right to us, what strikes us as fair and just and righteous, really is in some important evolutionary sense what _is_ right for us. Our job is to understand and develop that, just as we understood and developed medicine, law, and all the other sciences that have improved our lives.
Religion, on the other hand, throws in the towel at the outset and proclaims that Man is irrevocably broken and only a miracle can fix him. How much hope is there in that? I don't know about you, but I'd much rather bet on science than miracles. And so would every person whose live has been saved by antibiotics, vaccines, and organ transplants. Heck, my own life has been significantly prolonged by a fifteen-cent pill (I am a diabetic). Maybe you're one of the lucky ones that God blessed with perfect health, but I'm not, and frankly, if I were relying on God to save me, I'd already be dead.