I wouldn't say that emotion is man's greatest fault. But I do think that they are over-rated by our modern society. The idea of being logical is looked on as being "cold" and "inhummane". To me, emotions are just evolutionary mechanisms, which would have preceeded rational thought and intelligence. Almost all of our emotions can be expalined in evolutionary terms.
Take for instance
fear. We will use the exapmle of two primitive humans wandering the jungle, having come across a ferocious lion. The first human has the emotion of "fear", sees the roaring beast with massive teeth, and gets scared. He immediately turns around and runs for it. Our second human, decides to consider the consequences. To logically weigh up his options given the situation. He quickly comes to the conclusion, that if he doesn't run away he is going to be killed. Unfortunately for him, it is too late, as the lion has already pounced on him!
Also, not only does the emotion of fear, encourage our first man to run away, it makes him run away faster. When we get scared, our hear starts beating faster, we start breating lasrge gulps of oxygen, and our body fills our bloodstream with endorfuns and adrenaline, all of which is beneficial to us for running away. These endorfuns can give us quite a "buzz" which is why we love to get "scared" by horror films and rollercoasters and the like. We "logically" know that the horror film can't hurt us, but we don't
emotionally know it, hence our bodygets scared, and we feel excited and feel the "buzz" from the natural drugs in our blood.
It has also been suggested that the reason that you "shit yourself" when you get
really scared is so as to make your body as light as possible, again to aid you in making your get away.
Or take what is commonly described as "our most powerful emotion",
love. Well consider who it is, that our love is most strongest for: our sexual partner, and our children. Both of these people are vital, in order for you to achieve your ultimate purpose in life; pass on your genetic material. So in essence, you feel a very strong need to protect these people, and ensure no harm comes to them, so you "love" them.
Or take even the emotion of
disgust. Again, we have two primitive humans. this time them come across a hunk of rotting meat. The first human sees this and "knows" that it is disgusting, so turns and walk away. The second "logical" human looks at the rotten meat. This meat doesn't look the best, but he's pretty hungry. He comes to the logical conclusion that old meat is better than no meat at all. He of course knows nothing about hyegine, or bacteria, and doesn't realise that eating this rotten meat will make him ill.
So emotion is a by-product of our evolution. Like ART said, its important to ackowledge that your emotion is there, but letting it rule your life, or letting it "over-ride" the logical part of your brain is not a good thing.