Born again Christians believe that if we were judged based on our actions alone, all of us would go to Hell because we're all sinners. The only way to avoid this is to accept Christ's sacrifice and all sins will be washed away. If you're the kindest, nicest, most moral person who ever lived, but you don't accept Christ, you go to Hell. If you're the rottenest, meanest, most sinful person who ever lived, but you do accept Christ, you go to Heaven.
There's no point in doing good deeds or avoiding sin. As long as you have faith that Christ died for your sins, you can do whatever you want. This idea really isn't that different from other forms of Christianity which teach that you shouldn't sin, but if you do, you can just repent and it doesn't count. The extreme form of this is the death bed confession, where an entire life of sin is forgiven at the last minute.
Why do Christians wonder where atheists get their morals, when we can just as easily ask where Christians get their morals? If repentance or even simple faith in Christ means you can do whatever you want without being punished, why be good?
Although they're not really enforced, a few states in the US have laws preventing atheists from holding public office, serving on juries, or being witnesses in a trial. If an atheist swears to tell the truth, you can't believe them. However, there's nothing to prevent a Christian from lying then repenting of it later; so in reality, you can't believe them either.
It goes without saying that every person, except for those who die very young, has committed at least one immoral act during their lifetime. It's also common knowledge that some people are more moral than others. There are moral and immoral atheists, moral and immoral Christians. Do these morals come from the Bible?
Both thy bondmen, and thy bondmaids, which thou shalt have, shall be of the heathen that are round about you; of them shall ye buy bondmen and bondmaids. Moreover of the children of the strangers that do sojourn among you, of them shall ye buy, and of their families that are with you, which they begat in your land: and they shall be your possession. And ye shall take them as an inheritance for your children after you, to inherit them for a possession; they shall be your bondmen for ever: but over your brethren the children of Israel, ye shall not rule one over another with rigour. (Leviticus 25:44-46)
There are numerous scriptures in the Bible which show that slavery is acceptable (Genesis 17:13,27, Exodus 20:10, Exodus 21:1-4,7-8,20-21,26-27, Deuteronomy 15:12-18, Deuteronomy 20:14, Deuteronomy 21:10-14, Deuteronomy 23:15-16, Leviticus 19:20-22, Leviticus 25:39,48-53, Numbers 31:28-47, 1 Corinthians 12:13, Galatians 3:28, Colossians 3:11). Yet, there are none that say the institution of slavery is bad (although keeping a fellow Jew as a slave is forbidden.) Yet, even the most orthodox believers in the truthfulness of every letter of the Bible don't practice slavery today.
If Christians get their morals from the Bible and the Bible says slavery should be practiced, how come very few Christians today believe that slavery is moral? The fact is, Christians don't get their morality from the Bible. Modern society decided that slavery was immoral despite what the Bible said.
The only way someone can get their morals from the Bible is to pick out the scriptures they agree with and ignore the scriptures they don't. Numerous passages in the Bible, such as the ones advocating slavery, are definitely not moral by modern standards. Both Christians and atheists rely on their own internal sense of right and wrong to tell them which scriptures are moral and which aren't.
Does this internal sense of what's right and wrong perhaps come from God? If so, you'd be forced to say that God changes, since our internal sense of what's right and wrong varies based on culture. Why else would God tell the ancient Israelites to keep slaves and tell modern people they shouldn't?
You might be thinking that morals really aren't different across cultures. Don't all societies believe that murder is wrong? Well, not really. Some cultures believe that killing is wrong no matter what, while others say it's OK to kill in self-defense, in defense of others, for the death penalty, during wartime, by accident, if someone has insulted your honor, etc. The Bible even says it's OK for a parent to kill a disobedient child (Deuteronomy 21:18-21).
I recently attended a debate in which a Christian argued that atheists only have subjective morality. Objective morality, he claimed, came only from God. He didn't explain what he meant by objective morality, so I'm left to guess. If objective morality is the same morality found in the Bible, then it's not moral at all by today's standards. If objective morality is our own internal sense of what's right and wrong, why wouldn't atheists have it and why does it change over time? Maybe he meant that to be truly objective about morals, one has to exist outside the universe and not interact with it. If objective morality exists outside the universe, then it's a moot point whether it exists or not since we have no way of accessing it.
If this internal sense of right and wrong doesn't come from the Bible or from God, where does it come from? Part of it comes from evolution. Animals who've never read the Bible or heard of God nonetheless perform acts of kindness towards each other. An ape who steals food gets ostracized and is less likely to reproduce than an ape who shares with the community. Kindness to others ultimately derives from self interest. You're nice to other people because you expect they'll be nice to you in return. Those who don't play by the rules get shunned by society. Those who contribute to society generally get rewarded.
Atheists and born again Christians are moral not because of religion, but because our society teaches us to be moral. The functioning of society is dependent upon the majority of people in that society behaving morally. A society in which rape or murder were acceptable would tear itself apart. Societies value morality because it keeps the people in that society safe. People practice the Golden Rule in order to ensure the inverse of the Golden Rule is also observed: Don't do to others what you don't want done to you.