I'd have to agree the most with 2.8. Surely a life worth living is one where it would be preferable to create an additional person who lives such a life, all else being equal, and therefore there is a great benefit to having very many people living lives worth living. The problem seems to be that the idea of a life only barely worth living is considered to be horrible, whereas surely if it would be horrible, it isn't worth living? I think this mostly arises from the difference between a life worth continuing and a life worth creating. The accepted view of suicide and euthanasia (especially in the US) seems to be that only the very worst, most painful lives should possibly be ended. Yet if you wouldn't have a child if it was destined to live a life in population Z, then surely those lives are not worth creating?