Lots of people think God makes things moral. When it turns out that there is no God, many atheists think there is no morality after all. They still avoid terrible evils and so on, but if you ask, they’ll say that they don’t believe in any morality. See “Secular Morality” on the main menu for an explanation of why morality is objective, without anything supernatural.

On a less philosophical level, atheists who used to think things were wrong for religious reasons will often jump to conclusions. They’ll start believing that those things are all just fine, before they closely re-examine them.

Some new atheists are too quick to abandon old moral ideas, so they often make mistakes. They learn from their own mistakes instead of from the mistakes of others. After a bunch of mistakes with alcohol, drugs, sex, dishonesty, unkindness, selfishness and so on, they’ll figure out a set of rules that help them avoid regret and sadness and so on.

I recommend that we not make any big changes to our moral rules until after we’ve examined them carefully for any possible flaws. Are there reasons to be honest even if there is no God? Are there reasons to be kind, or altruistic, or to have some level of restraint with drugs, alcohol, and sex? Look it up. Found some? Great, now look for more. Be careful. Have some prudence.

If your moral foundation has been pulled out from under you, that doesn’t mean you stop worrying about morals, it means you have to go through the work of rebuilding the whole moral structure again from scratch.

Except, it’s really not that hard. People have already done the work for you, you just have to take the time to look it up and think it over. You can find “a discussion of prohibitions you may want to follow even when you’ve thought of a clever reason to think they don’t apply” at Ethical Injunctions.

See the “Secular Morality” section for some moral teachings, as well as how things can be objectively moral without a God.
See “Failures of Atheists (to Avoid)” to find other errors (to avoid).