I am sure that if God could ever justify having to kill someone to protect Himself and us, neither Him or us would have any regrets.
But I do not think for a second, He would ever dishonor Himself by admitting they were beyond His power or repair, and posed a threat He could not handle or solve without destroying them.
God is Andy Griffith, NOT Barney Fife.
Eternal humilation and shame of those who oppose, is a much bigger gun than eternal destruction...plus it provides entertainment and an useful example to others watching.
Would you kill your volunteer examples?
That would be wastful and counter productive.