The problem is that people can't imagine life without their god or Big Brother and they don't realize that they don't actually need this authority figure. I insist that my morality comes from common sense and from our collective history as social creatures. Theists would counter that the morality I assume is from nature and social structure is actually from god, because god is the definition of morality. There's no real way to prove or disprove this, of course, but there are some good logic puzzles we can play.
There are two options: either god is the author of morality or he isn't. If he is, then anything he says becomes moral. If he isn't then he himself is capable of committing an immoral action. Let's assume that he is the author of all morality. This means that not going to church on Sunday and having lustful thoughts truly are sinful. It also means that, should he decide to do so, god could make rape a moral action. I'm not saying that he ever has or ever would, but let's just pretend. Suddenly rape would be moral. I would be immoral for not committing rape. Christians have no choice but to agree that if god suddenly appeared and told them to rape they would do it. They might point to the Abraham vs. Isaac story, calling it a test of faith or proving trust in god. The problem becomes evident. Morality is arbitrary and 'being good' simply means being obedient. And arbitrary morality is exactly what theists accuse atheists of. If god is not the author, then it doesn't really matter what he says.
So what about me? Where does my morality come from? From myself. I make my own judgments. Everything has to go through my own morality filter. I do wish that there were an absolute rule, but there isn't. Life is too complicated. My latest thoughts of morality have been informed by Peter Singer, where suffering is a major consideration. It isn't a perfect system, but it works for now. So, in my head, eating meat is largely immoral, but lusting after my neighbor's wife (or just women on the internet) or coveting my neighbor's items is perfectly healthy and normal.
If everyone is their own morality filter, then why on Earth would anyone trust an atheist? Why would you trust me with your money, your secrets or your children? Why would you trust anyone? If I betray your secrets I lose your faith. If I steal your money or damage your children, I lose my freedom and self respect. Believe it or not, I don't actually want to kill, rape and steal just because I won't be punished in the afterlife. Punishment in this life is enough for me. In fact, Christians simply have to pray for forgiveness. Look at the Catholic Church! Pedophile priests are an actual thing, causing untold damage to countless children every year. There's really no incentive to be a good Christian. For an atheist, this is the only life there is. And hurting others is not the best way to enjoy it.
Are there bad atheists? Of course there are. But a quick peek at religious affiliation in prison populations shows that atheists are underrepresented. according to this study, atheists represent about .2% of the prison population vs. 8-10% of the rest of the population. This poll is dramatically out of date and I cite it only for illustration purposes. Even if it were commensurate with the population it would make my point. If atheists are not more moral, then they are certainly no less moral than the standard Christian American.
I am a good person. When I die it won't matter. But I am a good person now because I value life and comfort and fairness and happiness. I want to make the world a better place. Why? I don't really know, but I'd imagine it's for the exact same reasons that anyone else has.