Saying that there is no morality without God/religion makes about as much sense as claiming that there can be no morality without government

Many religious people often claim that morality cannot exist without God or without religion. I'd argue that this claim makes about as much sense as arguing that morality cannot exist without government.

So God in most religions is an authority figure who decrees certain things and threatens to punish those who disobey. Equally government is an authority that decrees that people must behave in certain ways, otherwise they will be punished.

But just because something has been decreed by an authority does not mean that such a decree is morally good, or that morality cannot exist in the abscence of such a decree. So if the government says that all drugs are bad and should be banned, does that mean that all drugs are therefore bad just because the government says so? Of course not. Sure, certain drugs may be bad, but they're not bad because the government says so, they're bad because they cause harm to drug users and others. And is it impossible to form moral frameworks about drug use in the abscence of laws prohibiting or permitting drug use? Of course not. Even if there were no laws regulating drug use we could still make observations about whether certain drugs are good or bad. And is government automatically a morally good actor just because they have the authority to decree certain things? No, of course not. Governments can issue laws that are inherently immoral and wrong, not all laws are automatically good just because they are decreed by an authority figure.

And it's the same with God. If there were no divine decrees relating to the concept of slavery for example does that mean that it is impossible for us to figure out whether slavery was good or bad? No, of course not. Even in the abscence of a divine moral decree we can still make judgements about whether something is good or bad. And if God issued a certain moral decree does that automatically mean that said moral decree is automatically good? Also, no. The concept of God does not auomatically imply that such a God would be a good and benevolent being. A supreme being or a God could very well be inherently cruel, evil and malevolent. Just because a God issues a certain moral decree does not mean such a decree is good.

And finally there is also the possibility that a God exists, but just isn't interested in humanity at all and has no interest in communicating with humanity. The God of Deism would be such a God, meaning a God who may have created humanity but who does not get involved in human life and who does not communicate with humanity. A deist God may never communicate with humanity at all, so does that mean that we couldn't ever know what behavior is good or bad in the abscence of divine laws and communication?

No, just like we don't need require government to figure out right from wrong, equally we don't need God to figure out right from wrong. The only thing that morality requires is a willingness to figure out right behavior from wrong behavior. So I'd say the only prerequisite of establishing a sense of morality would therefore be genuinely caring about other people, and other people's well-being or misery. So that means that a full-on psychopath who truly doesn't give a flying f about other people's feelings won't ever care about right behavior beyond the scope of potential personal punishment or reward. On the other hand someone who cares about the lives of others, and other people's potential well-being or misery will be inherently motivated to form a coherent sense of morality.

So morality simply requires caring about other people's feelings and other people's potential well-being or misery. Now, trying to figure out what constitues right behavior and what consitutes wrong behavior that will often be subjective. On some questions like slavery, murder etc. humans largely agree these days, yet on other moral questions we still have extremely different opinions. But God does not change that. The existence of morality is not inherently tied to the existence of a God. A God himself can be a good and benevolent entity but he could also be an evil and malevolent entity. Or God could just be entirely absent from human life, e.g. a Deist God.

So figuring out what is right behavior and what is wrong behavior does not require the existence of a God. It merely requires caring about the wellbeing of other people.