it is and yet, I feel certain Laufey would have been like "what gives him the right to keep my people down. What gives him the right to keep my people from expanding and growing across the cosmos?" So order is needed and leaders are necessary in order to keep the peace, even on Midgard, because we have people like Laufey here too, who would use bloodshed in the furthering of their own group.
The moment you say it is unquenchable, it kind of does go into one dimension villain land. I'm sorry it really does. Because once there is nothing that will satisfy or stop it, all the deeply rooted pain that those feelings came from is obsolete. it means nothing at that point, and the character has lost all humanity.
Think what I said about Faith on Buffy a few posts ago, certainly there were moments that people could have wondered if her hatred jealousy and need to harm Buffy was unquenchable, but yet she did stop hating Buffy and find that peace in the end. That's what made her a great character and a great story arc, and not just purely and simply a villain.
I wish I could remember better what happened with Callisto and Xena on that series too, they managed to redeem her in an interesting and different way, and of course Xena herself committed some atrocities before becoming a hero, and yet she was always troubled/tortured by her acts from the past (a big part of which is where Callisto as a villain came from).
In regards to Thanos and Death, from my understanding from what I've read, if he received Death's love somehow then that thirst for killing may very well be quenched. He would no longer feel the need to impress her by killing everything for her because he thinks that's what she wants, he would have her love already. he may still have desire for power but he would likely no longer feel the need to kill indiscriminantly. So in that way, I dont think that Thanos' need to kill is unquenchable. But from my understanding of her character, what he doesn't understand is she doesn't want the death of all things, she wants balance for the most part, with perhaps a slight advantage to her sometimes, because if all things are dead, then she has no place in the world herself, nothing for her to do, similar to the story where nothing dies. There was also reference in a character bio to Death not being able to stand suffering, which makes sense since suffering often ends in Death. So the suffering that Thanos creates (such as with his "granddaughter") horrifies her, but he can't understand why it wouldn't impress her. Or why him being all poweful wouldnt impress her, she wants balance in all things, even their potential relationship.
So it's an endless circle for them, unless Thanos can suddenly figure out that what she wants is balance and he needs to keep that balance for her so she will love him (and that doesnt mean killing *everything*). So I believe her desire is balance and Thanos doesn't understand that about her and so keeps going about wooing her the wrong way, just as Loki keeps trying to do the right thing to impress Odin but in the wrong way. The question is can Loki or Thanos ever accomplish their goals in the right way? And that is what makes them multidimensional, btw, not just a tragic past and wounded emotions, but as soon as you say that nothing will quench that desire for revenge or killing, *absolutely nothing* that is when they go into 1 dimensional villain land again, no matter the past.