That's another thing I should've brought up in the OP, since I'm a moral nihilist, I'm rather hoping this won't be an exclusively ethical debate. Factual analyses of the outcomes is probably the best thing to look at. And overpopulation due to lack of deaths is something I considered as well. So there's one limit we'd have to consider, nothing that would upset the cycle of life and death in a way that would cause unmanageable population growth.