Well, that model may be stable (I haven't actually thought it through sufficiently to judge, but let's grant that it is) — but how exactly is it "fair"? I mean, you're assuming a set of values which is nowhere near universal in humanity, even. I'm really not even sure what your criteria here are for fairness (or, for that matter, optimality).

My problem with what you describe is the same as my problem with what shminux says in some of his comments, and with a sort of comment that people often make in similar discussions about immortality and human lifespan. Someone will describe a set of rules, which, if they were descriptive of how the universe worked, would satisfy some criteria under discussion (e.g. stability), or lack some problem under discussion (e.g. overpopulation).

Ok. But:

• Those rules are not, in fact, descriptive of how the universe works (or else we wouldn't be having this discussion). Do you think they should be?
• If so, how do we get from here to there? Are we modifying the physical laws of the universe somehow? Are we putting enforced restrictions in place?
• Who enforces these restrictions? Who decides what they are in the first place? Why those people? What if I disagree? (i.e. are you just handwaving away all the sociopolitical issues inherent in attempts to institute a system?)

For instance, you say that "each living entity would get to have" so-and-so in terms of lifespan. What does that mean? Are you suggesting that the DNA of every human be modified to cause spontaneous death at some predetermined age? Aside from the scientific challenge, there are... a few... moral issues here. Perhaps we'll just kill people at some age?

What I am getting at is that you can't just specify a set of rules that would describe the ideal system when in reality, getting from our current situation to one where those rules are in place would require a) massive amounts of improbable scientific work and social engineering, and b) rewriting human terminal values. We might not be able to do the former, and I (and, I suspect, most people, at least in this community) would strongly object to the latter.