It's all an emotional mask for the horror and dread that many people have about death. I think that the main difference between atheists and theists is that atheists do not let their mortality frighten them. In foxholes and on battlefields, the atheist is less likely to break down and pray to a god for divine help, and more likely to anylize the situation and try to find the way to safety that works for them. Of course, I do not assert that all atheists are braver and more rational under stress than theists, nor am I implying that all theists are quivering lumps of irrational cowardice. Likewise, the question of justice is another aspect of life that poses a serious problem for a theist.
History is replete with tyrants who lived and died unpunished for their evil deeds.
Many times, we do favors for people that never get repaid. Sometimes, good people die without ever getting a break from pain. This problem is often referred to as the question of ultimate justice by Christians. Evil people are taken care of after death by being sent to hell to suffer eternal torment for their wicked ways. They cannot admit that sometimes, all the effort you put into justice amounts to nothing.