Christans: why is the concept of someone doing good w/o being motivated by fear so offensive to you?

I'm not offended at all by atheists who do good deeds. But in reference to what you're saying, just remember that not all Christians are alike. Yes, there are those who get defensive when their faith is questioned, but that's not the proper way to handle it. However, as I've said many times "Christians aren't perfect, just forgiven.