That's not right. Killing people in combat is something that is an unfortunate necessity, but should not be sought after or celebrated. Purposefully wanting to hurt people means that you probably have some issues that need working through.
Unfortunately, if you join the army, you won't be alone. Plenty of soldiers feel the way you do - they generally tend, however, to be a minority of soldiers and they also generally tend to get into trouble.
Being a good soldier and a halfway decent human being means you have to follow the rules of war. If you really just wish to "fuck up" people with knives and bullets, then you need to consider whether or not you have the discipline to follow the rules of war.
I dislike fundamentalist islamics. I do not wish for them to be killed - I'd rather they put down their weapons and go live a nice, normal life. I realize that most of them won't and that, unfortunately, we will have to kill some of them. But I don't leap to the conclusion that we must "KILL THEM ALL" straight away. I don't like killing, necessary as it is sometimes. Soldiers, good decent soldiers, should not like killing either (and most don't). Soldiers should not feel ashamed of their actions in war (provided they were carried out legally), but they should never feel happy that they killed other human beings.