You should have been there. You could have handled it perfectly, and healed the man so he sinned no more.
You seem to be bothered by the notion that preserving life and working to restore someone to mental health and dignity are good things.
Murder should not be condoned or defended simply because a government employee holds the gun.
The only being who should be cheering about situations like this is the Father of Lies.
It is he who does not see the value and inherent dignity of men as image bearers of God.
When government employees fail to view their employers as having the same dignity, they serve the will of the Father of Lies.
When people cheer on the murder of someone claiming to be suicidal, they also serve his will. The Enemy delights in death and destruction.