That's also true. Even if it would make us feel righteous to liberate so many... what would happen then? Radical change would only cause upheaval, if there is nothing to support and uplift the Monsters in the aftermath. They would know not what to do with their new freedom. The Witches, then, could easily coerce them to return to their bonds.

[one could say they'd slip back into chains or something like that...]

This mission needs to be the start of a long term revolution. A slow burn, not a flash fire.