How do you know that? Some pretty miserable people had finite lives too.
> Take away death and what do you get?
I don't think they'll forbid people to die. It will simply become optional.
As for more practical objections to your opinion - when you're young you live like you're going to live forever. I don't think kids and young people live less happily than old people.
You can't even euthanize yourself in most states. If you want to die, people consider you 'insane' and you get locked up at the govt's (and your) expense.
Life extension / artificial age reduction will purely be a benefit for the rich - the poor will just get injections so they live longer and work harder for their ageless overlords. It's not gonna be good.
http://www.imdb.com/title/tt1637688/
Just because you can't age doesn't mean you can't die. I think if people started living forever there would be a lot of rebellion from the people who are not given that access. Assuming at that point they can't just use brute force to protect themselves from the masses.