Atheists/humanists such as myself are often confronted with the thesis that morality can only exist by an act of divine fiat, that without commandment a person is simply making up their own moral code and therefore will simply be doing what they feel like and perhaps justifying it with argument.

There are numerous threads touching on this subject in this and in the atheism subforum. Here are a couple:

I was brought up Jewish. Morality in Judaism is a matter of contract. God made a covenant with the Jewish people. They're supposed to follow the Law and God will be their god. It's pretty straightforward and leads to a lot of argument about what following the Law entails.

The ethical complications arise in whether or not the decision of my ancestors is binding on me. Modern Jews come to their own conclusions on this matter with a distribution of outcomes stretching from Ultraorthodoxy to complete atheism.

Jewish folklore has a concept of place in the afterlife with a sense of better places for the more observant, but it isn't strictly a tenet of the religion.

Others, e.g. Christopher Hitchens, have argued that a religion with salvation is like an authoritarian regime. Hitchens was fond of saying that at least in North Korea you can die to escape the authoritarianism.

I don't think it's necessary to go that far to find a problematic element in the concept of salvation.

That element is that salvation is, for all practical purposes, unimaginable.

Many religions have had afterlives that were imaginable. They were better than this life quantitatively, but not qualitatively. The ancient Egyptians imagined an afterlife where the people were still growing crops to eat but the crops never failed, no bugs, no diseases, no famine. It was this life but better.

But salvation as currently conceived is a state that human minds can hope for without being able to conceive of.

On the other hand, the opposite of salvation, damnation, is easy to conceive of.

Damnation as a matter of writing is simple to depict. Human life has a lot of misery in it. All one needs to do is escalate aspects of that misery (whether it is torture, boredom, the company of jerks, etc.) to create an easily identified hell.

Dante had no trouble depicting a panoply of suffering, but struggled mightily and admitted his failure at creating an image of heavenly bliss.

In practical terms religions focusing on salvation inspire images of damnation. They create a focus on failure to live up to the tenets of the religion and a fetish for the suffering that will befall those who do not do so.

This creates a bias towards viewpoints that are both judgementalist and triumphalist.

In this state of mind people are more likely to be self-righteous and hypocritical. The more certain they are of salvation and the more afraid they are of damnation, the less likely they are to try to act morally.

This is problematic since it's clear that at least one purpose of the ideas of salvation and damnation is to create the kind of introspection and careful action that leads to humans acting morally toward each other.

Some would dismiss this argument by saying that no true insert-religion-name-here would misuse these concepts like that, that a seeker after salvation will work to do good for other humans.

I don't think that's relevant. The question is not whether there is a right way to do this. The question is, does teaching these ideas generate a greater likelihood of human morality or human immorality?

I would argue that because salvation is nebulous and damnation visceral, that the teaching of salvation as a concept does more actual teaching of damnation.

Damnation thinking does not get people to behave themselves. It creates judgment, one-upmanship, and suffering among people who are told that their human thoughts and actions are damnable.

Damnation-based religions are clearly not generators of human morality. History shows they are are continuous generators of human suffering.

The question becomes, is there a way that a salvation-based religion can be stabilized so that it won't mutate into a damnation-based religion?