The idea of dispelling guilt by killing an animal is garish enough. Doing so by killing a person is the sort of thing we might expect from primitive people striving to survive in harsh environments.
In any case, the understanding is that Jesus sacrificed a human life. His human persona did not sin, and since the wages of sin is death, he paid a penalty for a crime he did not commit. So the value of that life is applied to those who have committed the crime (sin, in all of its forms), and it is available in perpetuity. Since he is God (or God's son, depending on your beliefs), that sacrifice is not limited to a one-time or one-person use.
If it doesn't make sense... I didn't come up with it. A human society that now had the time to wrestle with much more complex concepts of life/death and good/evil took a few shots at it, and some of their efforts made it into the Bible. It's still barbaric, but we must remember that these were people who fed one another to wild beasts as a form of entertainment meant to keep the masses pacified.