Somejew,
Question: Why can’t we use iron on the מזבח? We are told it’s because iron is a tool of death. But isn’t it used for the killing of bad people? How can death itself be something bad, sometimes it is a very good a necessary thing?
Another question: Dovid Hamelech was not able to build the Beis Hamikdash because דם לרוב שפחת – Hashem didn’t want His house built by someone whose hands were filled with blood.
But wasn’t it the blood of wicked enemies of the Jews who deserved to be killed? What could negative about this?