It wasn't unavoidable insofar as both Chris and Barb burned their bridges with their families. You can't forcibly commit Chris short of him presenting a credible threat to himself or others... and apparently macing someone over cartoons wasn't suffucient. And if Barb chose to live with him while she was still lucid, that wasn't in anyone's control either. Nobody cared about either of them, and while that in no way makes what Chris did anyone else's fault but his own, it created a situation where two adults who legally were not deemed dangerous or incompetent could live together and foster this situation.