I'm not sure you understand. No one is perfectly good except God. All humans were created by God and have knowledge of good and evil. So have the capacity to do good and the knowledge of what is good. I doubt any Christians would say that non-christians cannot do good deeds.
Well, you obviously haven't been in the Christian churches I've been in
Given the wide variety of denominations, of course, I'm sure my small experience cannot speak for every Christian. But I have definitely heard the sentiment.
About your bit on their being no absolute morality, I hope you're not suggesting that evolution preaches that because science doesn't moralise.
No, well, evolution doesn't preach anything. It merely provides an explanation for the existence of morality. And that explanation doesn't allow the possibility of absolute morality.
There are also a couple of good arguments against the existence of absolute morality, evolution or no. One is that no matter what moral system you believe in, there are always going to be morally-ambiguous circumstances. Another is that definitions of morality have changed over time within the same culture, and vary greatly among different cultures, even among those that believe in the same religion.
A good example of moral ambiguity is killing. This is a natural moral code that is common the world over, but not in all situations. Consider, for example, that the vast majority of people would consider it okay to kill if that person is in the process of attempting to kill you. And one could come up with a myriad of in-between situations where few would agree on the correct behavior. For example, is it okay to kill in defense of family? In defense of friends? In the defense of strangers? In the defense of people with whom your culture is highly antagonistic (imagine a Jew saving the life of a Muslim by killing a Jew, or vice versa)? In defense of personal property? In defense of others' property? To prevent your own rape? To prevent the rape of another?
A good example of moral change through history is public decency. Consider the Victorian era in England:
http://en.wikipedia.org/wiki/Victorian_morality
Many of the things they did we would today consider indecent, others we consider overly prudish.
A good example of moral differences over different people within the same religion is abortion. Many Christians believe that all human life is sacred, and thus we shouldn't murder unborn children, for any reason. A significant number of Christians, however, believe that we shouldn't ever force women to go through the pain, discomfort, and even suffering of unwanted pregnancy and birth to protect what isn't even a life, but rather a potential to become life.