Can an atheist really be good?

Those are not at all to be tolerated who deny the being of a God...promises, covenants, and oaths, which are the bonds of human society, can have no hold upon an atheist. The taking away of God, though but even in thought, dissolves all.
- John Locke, A Letter Concerning Toleration
But can a person who does not acknowledge that he is accountable to a truth higher than the self, external to the self, really be trusted?
- Richard John Neuhaus, Can Atheists Be Good Citizens?
The Russian novelist Fyodor Dostoevsky is often quoted as saying, “If there is no God, everything is permitted.” Similarly, the French existentialist Jean Paul Sartre has allegedly opined that "If there is no God, the only honest response is despair." We will allow those continental notables a bit of slack, as the exact sources of those quotes are difficult to pin down. Still, despite anything else those thoughts certainly convey ideas about atheism which an honest atheist should find hard to dispute.
If there is no God, everything is permitted. Sartre taught, rightly, in context, I would argue, that with no God each individual is god. Without a God of some sort as a philosophic basis for thought and action then everything is indeed permissible. The individual would have no need to consider other persons' rights. There would be nothing to measure them against if life, the universe, and everything were merely a personal domain.
Atheists will argue that this isn't true. An atheist can care about others, about right and wrong, about being responsible for themselves and his fellow man. Yet if what Sartre and Dostoevsky say is true, then the responsible atheist is being good only because he either isn't a real atheist or is, at the least, simply choosing to live better than his ideals require.
Why should it be any other way? An atheist after all believes (he must believe this as, again, a logical extension of his nonbelief) that we are accidents of the universe who came into being quite out of our control and will leave existence behind in a like manner. Where can you infer responsibility from that? You surely can't find dignity in it either.
I should point out that I am not talking about what many if not most atheists say atheism is but about where atheism, if true, must lead whether the adherents accept such conclusions or not. I will not dispute that most atheists lead relatively good lives. Yet that doesn't prove that atheism is true any more than a cold blooded murder by an avowed Christian would disprove Christianity. While it is generally good advice to question practitioners of given creeds when you want to find out what they believe, this cannot mean that they are in fact right about what they assert. There is a self interest involved in any creed, even Christianity, which may itself cast doubt on the veracity of the creed.
If atheism is true then the atheists who pay their bills on time, respect others, and plan for the future do so either because they're better than their premise requires or are just selfish about their comfort. There really are no other explanations for the 'good' atheist.