what are we supposed to say again when christians ask us where we get our morality?

[Tonus]

I can empathize and sympathize with others, and I would not want to be killed. I am aware that some people kill themselves, but usually it is because they are in a poor state of mind. Therefore I think it's reasonable to think that people do not want to die, and that being killed is bad from that standpoint.

…so goodness is defined as whatever people want?

I suppose that --barring a lot of context-- most individuals would consider getting what they want as a good thing.

I think there are two levels; that of the individual, and that of the society or community. A person on his own can use his sense of empathy or sympathy and his life experiences to form opinions on what is good or bad, or right or wrong, and these provide his moral framework. The more isolated he is, the more varied those might be. A society forms laws and cultural attitudes in a similar way, but they do so more via committee. It probably takes longer for a society to determine a set of morals, but those can also be in effect much longer.

Are there any external standards that the individual or society should use to correct and alter their moral framework with?

I don't know if there are any in particular that they should use, but I think that it can be beneficial for a community or society to examine others to see if there are ways to improve their own laws, customs, morals, and/or ethics.