I would not agree with euthanasia for anxiety/depression. Our emotions and feelings may change over time and so it is possible for someone’s situation to improve. Personally, my anxiety has reduced significantly compared to my mid 20s and I am now in a good place. I would like to think there is hope for others too. Just my opinion
You are right that emotions and feelings can change. A genetic defect cannot change. Those also cause anxiety disorders and depression.
Anxiety and depression are not just a wrong way of thinking or an unpleasant experience to get over. That can undoubtedly also be a cause, but certainly not the determining one in many people.