In אבינו מלכנו, among other places, we ask HaShem, "נקום לעינינו נקמת דם עבדיך השפוך", which roughly translates to, "let us see You avenge the spilled blood of Your servants."
1) Why do we have a need to witness HaShem's vengeance on our enemies? Doesn't much of our faith tell us that it will happen, and isn't that good enough?
2) The rest of אבינו מלכנו is pretty peaceful (as are, if I'm not mistaken, most other prayer sets that make this or a similar request). Isn't this pretty much out of place?