Of course! I often see fellow theists claim that those who do not adhere to any specific religion cannot be moral. This argument has always perplexed me because, for one, we all have a conscience, so that right there shows that an atheist can be perfectly moral, or ethical. Moreover, most of what constitutes morality in religion, even Christianity, is culturally determined in the specifics by the individual's understanding (Romans 14:5).
Moreover, are all people of different religions "equally" moral? Different religions have similar core principles (no murder, theft - much like any secular law in society), but they often differ in some not so insignificant points. For example, there was no condemnation of cultic prostitution in ancient Near Eastern religions. In Jainism and Buddhism on the other hand, material possession is much more condemned than it is in Christianity, Islam, or Judaism. How do we compare these if we're to be so mathematical and technical? Whose code is more moral and why if we're appealing solely to logic and not the conscience?
This is why John L. Mothershead points out that right and wrong aren't true or false statements. In addition, he notes that the absence of a belief in free will does not entail amorality because some actions are ingrained in us, such as the process of decision. Or take this elementary example: "Don't think of a black cat":
To maintain such a view [that the rejection of free will entails amorality] would be to maintain that we cannot by our choices influence our lives at all. [Ethics (1967), p.9]
And no one would argue that, of course: neither the theist, nor convinced atheist. The result is that atheists cannot pretend that even without free will one would have a "choice", be it deterministic or not, and as a result theistic arguments regarding ethics preserve their validity (e.g. that the ends don't justify the means), without the truth of the presumption of free will. On the other hand, the theist cannot claim that the atheist or his philosophy is automatically amoral by definition, as often happens right off the bat.
The argument takes a technical tone when a theist brings up the fact that an irreligious person, be it atheist or agnostic, doesn't have a foundation such as the Bible to draw his morality from. Therefore, he doesn't have an objective starting point and is inconsistent in his claims to any kind of permanent, real morality, as it would be relative. Inkeeping with Godwin's Law, it's not long afterwards before comparisons between Nazis and the Holocaust emerge.
But although it's true that this would be a completely relative morality, it is a jump to assume that it's then impossible for this person to be moral and consistent as well as logical about it. Even tame animals, who have no conscience, feel guilt, so it's not like all of a sudden Hannah Arendt's "Banality of Evil" kicks in and every atheist secretly becomes a James Bond villain. For every person that's presumably systematically immoral for being irreligious, there's a person who's abusive because he's convinced that (his interpretation of !) his religious code necessitates a certain action at the expense of someone else.
Moreover, the Euthyphro Dilemma becomes unsolvable and dispels any notion that an atheist's lack of "objective foundation" means he cannot be consistent in his logic for morality, because what's God's objective foundation for morality?
Social Rules and the Conscience
I'm not denying that a religion whose emphasis is on peace and happiness can vastly improve someone's life as well as the experiences of those around him. And someone who doesn't believe in an inescapable punishment for recalcitrant wrongdoing is certainly more likely to commit acts that even he believes are unethical and socially wrong. That's certainly the case with anyone in history such as conquistadors who felt free to pillage and plunder in the early days of the discovery of America under the excuse that they were already baptized Christians. Indeed, a tribal chieftain whose people were persecuted was asked shortly before being burned alive by a "pitiful excuse of a priest" as de Las Casas put it, whether he wanted to repent and go to Heaven. The chieftain asked where his persecutors would go. "Heaven," the priest responded. So the Native American chief said he wanted to go to Hell to not be with them.
But the very question here is whether a person can have a solid basis for morality regardless of religion. In that sense, we're asking the question from a social point of view, because we're dealing with it from the point of view of logic and results, not theology. In that sense, a "good" person can socially exist just as Paul uses the term in Romans 5:7. It's not because the unbeliever or religious adherent in question is incapable of being logically or realistically moral; it's a refusal of this individual to follow his conscience and/or social knowledge. But make no mistake: an intentionally irreligiously moral person is theologically just as impossible outside of our social constructs as an intentionally religious immoral one. This is why the infamous Psalm 14:1 actually says, "the immoral man says in his heart, 'there is no God'", as the NIV footnote tells us. The rest of that verse makes it clear: "They are corrupt, their deeds are vile; there is no one who does good."
Proof of this is the fact that many people have committed crimes without remorse, not because they were psychopaths, but because they willingly ignored the rights of others over their group's interests. For example, interviews of former German concentration camp guards consistently show men who genuinely did not consider their prisoners to be victims, but were brainwashed that they were helping Germany be rid of undesirables such as homosexuals, mentally handicapped, and of course races such as gypsies and Jews. The same is equally true of many during the Crusades who genuinely believed in the cause from a religious point of view. If a Christian objects to being blamed for what some did during the Inquisition, whether out of some kind of twisted or mistaken conviction, then an atheist can logically and rationally object to being called inescapably immoral or inconsistently moral.
Just because he's convinced of a different starting point from the theist's ideology so long as his conscience is clear on that point, it's no different; just like how in India you will offend a host if you reject anything he offers you to eat or drink, whereas in the West it's polite to relieve your host of your burden: a fact that was lost on the English guests of the famous mathematician, Ramanujan, which caused him to runaway for three days.
Legalistic Ideology versus Personal Knowledge and Understanding
Of course, I disagree with the atheistic notion that there is no objective morality, which isn't the subject of this article. I'm not denying the universal conscience's existence, but I am denying the claim that an atheist cannot be moral outside of strict adherence to a religious code. And if someone wants to say that an atheist can create some kind of personal morality that says it's ok to steal from the rich every now and then like Robin Hood, I again say that a Christian can be equally misguided in, say, his application of strictness from the Bible upon his children, for example (I'm sure many fathers misused and abused the "spare the rod, hate your son" verse from Proverbs 13:24).
This is also why attempts by non-theists to make a systematic relative moral system fail. The argument that "pain is bad; absence of pain is good," is not only untrue (e.g. studying is boring, and "out of the frying pan and into the fire"), but you'll rarely find two people who agree on any two things, including what pain is worse (losing your wallet or a broken car window). Not to mention when it comes to legislation and politics. These are simply things that you decide on a case by case basis, and are impossible and impractical to write down: that's not what systems were designed to do. This is why we have judges to interpret the laws, not just police to enforce them.
On the other hand, atheists shouldn't interpret Christian attempts to use this argument as a hateful personal attack, or as a Christian attempt to be "holier than thou". The reason most Christians appeal to this is usually just because it's such an easy cheapshot to win at something against the opposition. And the ideological distinction between theists and non-theists can affect some religious individuals most profoundly here because it's most visible since it relates most directly to their life and the things we have the most experience with: other people and their bullcrap.
In conclusion, all of us who live in a society know what its demands are. Unless there's some kind of systematic oppression, whether popular (e.g. racism, sexism) or institutionalized (persecution of a group), given an organized enough state, few people would cross those boundaries. And it's almost always because of some kind of pressure in life, and not primarily because of religious ideology or lack thereof.