I agree with you that the article engages in sleight of hand; however, I disagree with you regarding immortality.

While I do believe that "living longer (assuming high levels of physical and mental health is always better" is too strong a statement, I would argue that "having the choice to live as long as you want is always better" is much closer to the truth.

There are many projects that I will leave unfinished when I die; many things I will never get to experience. If I had the choice to live long enough to finish everything I wanted to do, I would gladly take it. I fully expect that, by the time I'm done with all that stuff, I'll find a lot more stuff that would require even more of my time -- but I could be wrong, in which case I'd want the option to end my life voluntarily.

I fully accept that there exist people for whom 80 or so years (or fewer) would be enough. Perhaps they lead much more efficient lives than I do, or perhaps they lack imagination or curiosity, or perhaps their lives are so terrible that death would come as a welcome release. But I have difficulty believing that the majority of people are like that. I'm pretty average, so it seems more likely that most people are like me.