Metal Created to Kill?

Question

Rashi at the end of Yisro (Shemos 20:23) quotes the Mechilta/Mishna in Middos (3:4) which says

הַבַּרְזֶל נִבְרָא לְקַצֵּר יָמָיו שֶׁל אָדָם, וְהַמִּזְבֵּחַ נִבְרָא לְהַאֲרִיךְ יָמָיו שֶׁל אָדָם, אֵינוֹ בַדִין שֶׁיּוּנַף הַמְקַצֵּר עַל הַמַּאֲרִיךְ - Since iron was created to shorten man's days and the altar was created to prolong man's days, it is not right therefore that that which shortens should be lifted against that which prolongs.

What does it mean that iron was created specifically to shorten the life of man? Meaning, I thought it was potentially dangerous force which could be used for good endeavors or the opposite, yet this Chazal tells us iron was particularly created for killing.

Answer 1

Perhaps it's a reference to what metal was first used for when it was first developed into tools. Rabbi Philip Bieberfeld in "Universal Jewish History", Vol 1, wrote:

"The development of human civilization was brought about by two different races, the descendants of Cain and those of Seth...It is highly significant that Cain, the first killer...became the first city builder. His new goal, of necessity, was to defend himself against a hostile world...He settled in "the land of Nod, on the East of Eden". This points to Elam...The choice of this country is easily understood as...Its deposits of ores, especially copper and lead, indicate, furthermore, that metallurgy was initiated there...Among his descendants, urban civilization experienced a tremendous expansion...The climax came with the rise of metallurgy, which is connected with the name of Tubal-cain, the first smith of copper and iron. This new art was soon misused to produce weapons of war. It is possible that the possession of such weapons inspired Lamech, the father of Tubal-cain, in his triumphal song which marks the appalling growth of the spirit of Cain." (pg. 62-63)

"Another city obviously connected with the descendants of Cain is mentioned in the earliest Babylonian king-list. Its name, Badgurgurru, means 'fortress of workers in bronze'; and it seems very probable that it was one of those founded by Tubal-cain, the originator of metallurgy...This would indicate that the descendants of Cain, after the discovery of metallurgy, conquered the land with their superior weapons and founded new cities (Larak, Sippar, Shurippak) among which a constant fight for supremacy raged until they were destroyed by the Flood." (pg. 68)

"It had already been pointed out that the descendants of Cain, obviously with the help of their superior metal weapons, had conquered the land. Their way of life dominated the earth, and for them life meant unscrupulous selfishness and the deification of power and pleasure..." (pg. 73)

According to Rabbi Bieberfeld, metals were used practically from the beginning to further warfare. As such, the art of metallurgy has since inherently been tied to weapons of death and destruction.

Answer 2

This may refer to the halachot of murder:

Bamidbar 33:16-18

Anyone, however, who strikes another with an iron object so that death results is a murderer; the murderer must be put to death. If he struck him with a stone tool that could cause death, and death resulted, he is a murderer; the murderer must be put to death. Similarly, if the object with which he struck him was a wooden tool that could cause death, and death resulted, he is a murderer; the murderer must be put to death.

The Rabbis learn from this that a tool made of stone or wood must be investigated to figure out whether it was likely to cause death in an ordinary case. So if someone threw a pebble, it took out someone's eye, and the victim got infected and died, the pebble-thrower would not be executed.

In contrast, any blow with an iron tool is always considered legally serious enough to cause death. If someone died from a poke with a needle (however unlikely that was to happen), it is considered murder (Mishneh Torah Hilchot Rotzchim 3:4).

In other words, ANY tool made of iron is liable to be a murder weapon that 'shortens one's days', unlike tools made of other materials. Therefore, as Rashi says, such a tool is not fit to be used to build an altar to Hashem.