I can't argue based on how the history is presented in FoV, since I have not played it yet.
There have been places and times when deserting from the army was punished by death. There was no great 'need' to kill any particular soldier for what may have been a temporary emotional state or possible extenuating circumstances, but that was still the policy. Undoubtedly there were people in charge who had some sympathy for at least some individuals to be executed, and yet followed procedure because they believed it was necessary - not that that person specifically needed to die, but that all deserters needed to be executed.
While you can argue about the appropriate punishment, I don't think anyone guilty of multiple murders is completely without blame if they were threatened to secure their cooperation.
The execution wasn't done in secret. They confronted Ygerna with the evidence against her, got a confession and carried out the prescribed punishment. Historically some people have been executed publicly as an example to others, and some have gotten lynched and hung from the nearest tree. During war, there are not a lot of breaks to have public trials.
Are you under the impression that somehow a women is incapable of being a zealot?
Show me one example of a female leader, who after dedicating her life to a single cause, is confronted with a trusted pupil (etc) who betrays that cause, and then responds by conceding that maybe everything she believed was wrong, and that her relationship with that person was too important to get in the way of the cause.
Damian's actions before Ygerna was executed were not particularly evil, but his response definitely was. Had he just attacked Lucien and the paladins you might be able to argue that he was justified. At some point starting wars, massacring anyone who gets in your way (or had any remote connection to helping anyone who got in your way), and attempted genocide stop being about justice and become just evil.
