The moral argument is one of the strongest arguments out there, because it is one that atheists cannot attack without proving. Put simply, if there is no God, there are no moral absolutes. Therefore, if you reject God, you cannot say "this is good" or "this is bad". This is especially true if you're a Materialist, because moral absolutes cannot be observed in the real world.
Or can they? Some atheists try to rescue atheism from the moral argument by pointing out that moral actions do have observable effects. We know violence causes pain, for example, and so logically we must shun violence. Right? Except no, that's a non sequitur.
To illustrate this, let's use the analogy of a match. You can observe the effect a number of moral actions have on a match. You can especially show that the match is destroyed if you strike it against a rough surface, usually the side of the matchbox. Yet, you cannot scientifically demonstrate the moral implications of striking that match.
The reality is, matches were made to be destroyed. The entire point of a match is to be struck in order to set it on fire, most likely with the intention of setting something else on fire. Thus, striking a match is actually a "good" thing. Now of course, we could complicate the issue by talking about the moral implications of why you are striking a match. It could even be wrong to strike someone else's match without permission simply because it doesn't belong to you. But all I hope to do with this analogy is to show that scientific observations, while they can show you the end result of an action, cannot tell you a thing about whether or not those actions are "good" or "evil".
But as I pointed out, purpose alters whether or not a moral action is good or bad. Matches are designed to be struck, therefore a good match is one that catches fire when intended. A bad match is one that cannot be struck without snapping, or one that just won't catch fire, or one that catches fire when it's not supposed to.
Just as a match can be judged by how well it performs its intended function, so also are we judged by how well we perform our intended functions. Morality comes not from science, but from God's own intentions. When we act as God intends, that is good. When we don't, that is evil. When we commit such evil, it is good that we receive punishments, even though we can observe that those punishments aren't nice. Or should we scrap law enforcement because criminals don't like it?
Unfortunately, we have all done evil, and so deserve punishment. However, God has a second option. He can extend mercy and grace to the sinner by directing that punishment somewhere else, namely to Jesus, the only human being who never sinned. All who confess Jesus as Lord and believe He rose from the dead will be saved. For those who refuse, the only good option left is that they suffer their own punishment.