Let me answer by analogy and then directly:
Posted on: January 3, 2020 at 11:25:31 CT
90Tiger STL
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By analogy:
If Person A murders persons B - Z, it is morally wrong for someone else to later murder Person A under the (false) pretense of "protecting the rights of" Persons B - Z. Those folks rights were already infringed upon, this is retribution and the further infringement upon Person A's rights as a reaction.
this is the same reason libertarians are against the death penalty.
Direct Answer:
Yes, it's morally wrong.
You conflated "stepping in" in your last sentence with later tracking down and killing the perp which was the actual scenario.
You did that either consciously to be dishonest, or subconsciously, to unwittingly display your lack of cunning.