Odyn is a Titan keeper and as such the opinion of mere mortals means little to him. He still considers Helya a traitor and never understood why she rebelled against him in the first place, which is a very good indication of what he thinks of the matter, by not giving a damn about her motivations.
Not to mention he does it to Ymmiron
http://wow.gamepedia.com/Quest:Ymiron%27s_Broken_Blade
Hero:"King Ymiron has been defeated. He fought fiercely."
Odyn:"That was to be expected. Ymiron was a cruel and evil ruler, but he always did fight with great ferocity."
Hero:"I want him to join our army."
Odyn:"Absolutely out of the question.
King Ymiron betrayed his people and doomed them to a cursed existence.
He might've died while fighting valiantly but I abhor him and the feeling is mutual."
Hero: "That may be, but what better punishment than to force him to serve you for the rest of time?"
<Odyn laughs a deep booming laugh.>
Odyn:"You are a devious one, <name>.
You are right, that would amuse me. Let it be done!"
Hero: "Thank you."