Input Field <-> Controller/ViewModel field two way data bindings are fine when they are kept simple, as I said in my comment. Two way binding is great for simple web form apps. If all you're doing is pairing a Name input field with a name variable on your controller or viewmodel, you're golden.

But having worked on complex dynamic form generators and enterprise apps at scale, I've seen the mess that KO observables and Angular $scope watchers create in practice.

Neither KO nor AngularJS actively encourage great patterns for data flow in their architecture design. It becomes all too easy, in some deeply nested directive or KO observable, to reference external/parent context or scope. React was specifically opinionated about this because Facebook hit real problems in production with two way binding.

Another benefit of one-way flow is that it becomes trivial to refactor your UI into modular components. Because the data flows in a top down manner passed in as props, it's easy to break up a complex component into several sub components.

React encourages you to fall into the "pit of success" by its design and there's very few traps.