For those who are not in the know, Extreminatus is when you basically destroy a planet's ability to sustain life, thereby killing every living thing on the planet.
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I'm not going to give you the bad of the scenario. I'm just going to tell you there are at least 5 billion sentient humanoid creatures with a situation that is getting out of control. It is the worst case scenario in your mind, whatever that is.
For fear of it spreading, for a Mercy Kill, to just be done with the whole thing... Could you destroy an entire planet?

Exterminatus
"Some may question your right to destroy ten billion people. Those who understand know that you have no right to let them live." — Exterminatus Extremis Exterminatus is the name in High Gothic of an action ordered by the highest authorities of the Imperium of Man to destroy an entire planetary...
I'm not going to give you the bad of the scenario. I'm just going to tell you there are at least 5 billion sentient humanoid creatures with a situation that is getting out of control. It is the worst case scenario in your mind, whatever that is.
For fear of it spreading, for a Mercy Kill, to just be done with the whole thing... Could you destroy an entire planet?