Whenever a manga/anime gets really philosophical, I always have to wonder anything is getting lost in translation. No insult intended to the translators, but there's a lot of nuance in English, and I don't know the nuance in Japanese.
Constance's declaration of "by any means necessary," sounds like a prelude to tragedy. (As is often the case in real life when people go that route.) As a heuristic, I would suggest caution whenever you find yourself falling into tunnel vision, where one single thing outweighs all other considerations.
Statistically speaking, and depending on the prevalence of different child rearing styles, about half of people tend to internalize ethical behavior, and about half of people tend to behave ethically as long as someone is watching to keep them honest. Then you're left with some remainders who have no empathy and will happily lie, cheat, and steal without any remorse. The nobility probably suffers from having people in the [as long as someone is watching] category with no one in a position to keep them in check, but there does seem to be a somewhat higher than average concentration of totally remorseless people in this particular group.
Honesty is the courage to not fear the consequences of your actions, and the confidence to not regret your actions.
And a side note on consequentialism:
"It is possible to make no mistakes and still lose. That is not a weakness. That is life." - Picard