This is the final post in my three part mini-series on dealing with the "how can you be moral without god?" accusation. I have tried to present some unorthodox approaches to this, for sure they are probably not original, anyway now I will deal with the two more obvious issues here, still, I hope, with some interesting twists.
To recap, I argued in The Crutch of God that such a question is a sign of a moral deficiency in the questioner themselves and so to place the burden of proof back with them and to avoid letting them change the subject. That is I used the metaphor of a moral cripple to throw back the accusation as in "I don't need the crutch of god to be moral, why do you?" (Not that you nor anyone would phrase it that way, that is up to you, of course!)
In my second post The Golden Rule Attack! I tried to highlight the plausible contradiction between subscribing to the Golden Rule, as at least a lightweight moral guide and the accuser making a morally bigoted statement. At same time by presenting an atheistic morality based on the Golden Rule, one can both again avoid changing the subject (to what you think morality actually is or is not) and also genuinely answer their question, without making any statements to defend, that is to give to the accuser a way out, not that they would admit it there and then, that they can be moral without god.
This leaves three outcomes which I think exhaust the possibilities, provided you have prevented them changing the subject.
First of all they may display some sophistication in discussing the Golden Rule and even criticising it, which implies that they have indeed thought about their moral position more than most religiously educated persons. In which case why have they made a knowingly false and morally bigoted accusation against you? Rather than making it a statement you have to defend, still remain Socratic and throw it back as a suitably formed question to them and don't make it final either, give them some room to manoeuvre. The chances are they are morally guilty of bearing false witness and deliberate deceit. Their response is highly likely to reveal whether this is the case or not. Again they have put themselves in a self-refuting position, although their self-deception will make them think they are innocent of this. If this conversation is amongst others, who hopefully have remained on the sidelines, another thing that you need to keep in check, keep the conversation on a one to one basis, they might see this better than the accuser. Regardless, remember this is not a conversation that is winnable but it can provide information to the accuser or onlookers that might sink in later or not. Either way you have not let them get away with it and have taken the moral high ground. These latter point also applies to the two others outcomes and so I will try not to repeat it again.
Now they may simply not have considered what they are saying. This is more likely in a random social setting, should it be speaker in any sort of public forum, it is incredibly unlikely that this is so and the first response above applies. They are guilty now of moral negligence and yes I do think it appropriate to emphasize "moral" here and in this whole conversation, regardless of your particular take on morality. The conversation is about their morality and not yours and so you are entitled to show the inherent contradictions in their position, using their own statements and nothing else, and this works regardless of your views on moral reasoning, relativism and non-cognitivism and so on and so forth. It is reckless, if not negligent, not to take reasonable precautions when your actions can adversely affect and harm others and when one specifically takes the position of being moral then one is morally negligent and that is the case here. Now you can ask, and it should be question again "I am puzzled, are you actually saying that it is only your belief in god that prevents you being a murderer, thief, rapist and liar?" This will lead to one of the other two outcomes I alluded to above.
I have had conversations with former drug addicts, as I found out in such conversations and, yes, they do believe that god alone has saved them from being a bad person. Well I certainly don't want them to lose such a belief and also now cannot trust them, what happens if they have a loss of faith, anything goes? I would terminate such a conversation by saying "I hope you do not lose your faith but should this ever happen please remember that you can still choose to follow the Golden Rule". Again, especially when in the company of others, keep to the moral high ground and any sympathy for the saved person will not detract from your sympathy for you view.
The final outcome, is, of course, that they do realise the naivety of their position and try an retract out of embarrassment, with inevitable diversions, no doubt. You have achieved a win in this case, don't go on to oversell your position and disprove god or blame their so called moral leaders for leading them astray. Instead try and make sure this point sinks in as in "Well I hope you don't make such a statement to anyone again, now you realised what you have said, lets move on to something more interesting". Leave it at that and move. My experience is that they will make it again and in your company, in which the gloves are off! Hopefully your mileage may vary :-)
A final point in all this is that I am assuming that you are not yourself guilty of moral bigotry, at least in such a conversation, and in the various atheistic and secular communities there are quite a few who are. The old adage two wrongs don't make a right applies. This mini-series was generated by one of my initial responses to this accusation namely "how can you be moral with god?". This is a legitimate question and one may of us I am sure has thought about. However in the context of the type of conversation I am analysing here, it can be equally taken as a bigoted view. It was in order to avoid responding in kind that led me to emphasize only using the accusers own statements including the deliberately provoked answers from my questions and assuming nothing else. This is my take on dealing with such a morally repugnant question, both this one and others. Use the socratic method, keep the burden of proof on them, assume nothing they have not said and prevent changing the subject. By doing this there will most likely be fireworks and histrionics but they have warranted and chosen such self-inflicted responses, you have not. Indeed everyone, whether they don't believe in god or do, should not let anyone let such moral repugnant statements go unchallenged. This way we can keep our freedom of and from belief and not let such freedoms be eroded - so that we end up feeling unable to respond to such statements - that is a world I and, hopefully, all of us want to prevent.