Freeing the spawn doesn't break the Oath of Vengeance either, FYI.

Honestly, it feels incredibly irresponsible to just unleash 7k hungry vampire spawn on the world. However, that does not justify murdering 7k innocents (or even one innocent, tbh), so for me they had to be spared. If I can see that Astarion deserves to be spared, and can survive without drinking blood from non-consenting people, then every single one of those other swawn also deserve to be spared, and they can survive in the same way.

That freeing the spawn breaks the Oath of the Ancients is, to me, an indictment of that Oath. It says that the Ancients dedication to light and life is less because those things are inherently good and more because they are Our Things. "We" are alive, and we are dedicated to those values. The Others are not alive, so they should be destroyed, no matter how innocent and victimised they are, no matter how much goodness they still possess in their hearts.

I chose Vengeance initially because I was basing my PC on a tabletop character I'd played, who was dedicated to getting revenge for her mother's apparent death. (I designed the Guardian based on the mother, whoops.) My PC's behaviour ended up being influenced by Wyll a lot, so she became more and more merciful as the game went on. It came as a huge surprise to me that she never ended up breaking her Oath. Vengeance allowed me to pick merciful choices, because punishing X character would have only been punishing the lesser evil, not the greater.

Anyway, back to the spawn. To me, the seriousness of the situation is such that we should be doing way more than just abandoning them to their own way. I mean, the Gur act as guardians of a kind, but there aren't that many of them. If we release those spawn (as we should), it should become our life's mission to help them make their way in the world.