Axel knew that Sophia and Isaac believed they were putting the safety of their pack first. The fact that they were saying this under the influence of the truth serum, confirmed it.
Axel could find justification for almost everything they did, but he couldn't accept that they gave away Talia when she was a baby. Even if they feared that she would destroy the pack, and there was no way to assure that wouldn't happen with her in the pack, they could have sent her to a safe place, to a place where they would visit and keep an eye on her, yet they just left her with a family of humans and didn't check on her until it was too late.
Two decades passed, and they didn't seek that family to see if Talia was alive? What kind of people do that?