I agree the other parent should step up. How do we know that Kaine didn't step up in this case? What shred of evidence has TH offered that Kaine just let her be drunk and didn't do anything about it? Oh wait... She hasn't offered anything against him, not one shred of evidence that he's a bad parent. If he was such a bad parent, there would be evidence of that, but so far, there's nothing.
We don't know the intricacies of how Kaine responded to Terri being drunk. For all we know, he was the best parent he could be under the circumstances. He was the only one providing a roof, food, clothes, etc., for his family. That means he was gone a lot because he had to be. So on top of that, he's supposed to fix all of Terri's problems like she's a kid and not his adult wife? Terri is the only one responsible for Terri.
For all we know, he did the best he could with her. Maybe he should have thrown her out or divorced her sooner, but really, would making a huge scene and battle out of it be good for any child? Maybe he was trying to make things work without it turning ugly in front of the kids.
And who knows, maybe she was lying to him about it or sneaking around drinking. As much as he was gone because somebody had to work, there's no telling what she was up to that he didn't know about. And with nothing before Kyron went missing to suggest she was a danger to children, was he supposed to make a wild leap to that?
People forgive an awful lot of things when it comes to those they love, unbelievable things. It doesn't mean they are bad people or bad parents.