How can anyone oppose voluntary euthanasia in the face of a story like this?
Here we have a rational, intelligent person who has decided that their quality of life will deteriorate so much as their disease progresses that they will be nothing more than a prisoner inside their own skull. But because of the current state of the law, they have to take a particularly slow and painful way out while they still can, because no-one will be allowed to help them later, and even those who simply provide the tools face prosecution for murder.
This is, at its core, a question of autonomy and authorship over our own lives. And as such, there is only one way it can be answered. We own our lives. They do not belong to god, and they do not belong to the state. The decision on when and how to die should (insofar as it is under our control) belong to us.