Hard determinism is a philosophical outlook which rejects the notion that human beings have free will. Hard determinists argue that free will is an illusion: free will is a subjective impression. We strongly feel as if we have free will, just as scientists once strongly believed that the sun rotated around the earth while the earth remained still, which we know today to be untrue. Free will is nonexistent precisely because every event is determined beforehand by forces beyond our control—be it social, economic, environmental, or biological factors.
This philosophy, deemed "incompatible" with the notion of free will, removes moral responsibility from our actions. If everything is preordained and we have no control over our own actions, how can we be held responsible for them? Punishment for offenses would thus not be justified, as it would appear nonsensical and even cruel to punish someone over something beyond their control. In the same vein, praise for making good choices would also not be justified, since hard determinists believe it wasn't your choice to make. A series of past events led you to make that choice, so it wasn't actually your choice. You had no say over the matter and therefore shouldn't be praised for good behavior.
Hard determinism has been criticized for rejecting ethical thinking and could be used as a front to condone morally reprehensible behavior. It would seem that this would then constitute an argument against hard determinism. As we do not yet have the means to prove whether or not humans have free will and that the hard determinists are correct, we should—for the time being—continue to act as if we do. If we begin to act and treat others as if they have no ability to grow and to become better, they won't have any desire to become better people. It will become a self-fulfilling prophecy and will excuse bad actions.