[Avodah] Questions about mechiyas amalek

[Rabbi@opengemara.org via Avodah]

On September 6, 2017 3:51pm PDT, Micha Berger wrote:
...
> A king can extrajudicially kill, but for an honest mistake?
> And yet no one discusses this as a sin on David haMelekh's part.
..
>: Yoav was a gadol hador?!  I don't see him listed in the Rambam's hakdamah.

> No! David haMelekh is the 6th name on the list. And how did someone
> at or rising to that level never discussed Yoav's shitah with others,
> particularly during the ramp-up time to the war. How is it DhM didn't
> get clarification /before/ the war?

The Gemara (Bava Basra 21b) says that the issue was "ארור עושה מלאכת ה'
רמיה [arur oseh melekhes H' remiyah -mb]" -- that the teacher should
be more attentive (also, it fits into the Sugya there -- that a teacher
who is medayek is better than one who's fast).

Also, there's a machlokes in Sanhedrin if Yoav was a good person who
made mistakes or if he was evil but found Dovid Hamelech to strong.