The point is this: if we had never heard of death, we would not take it on as a way of stabilizing the population.

That's probably true within a group, but I'm not so convinced that we wouldn't come up with death as a way to resolve arguments with other people.

Though, given that people would know that they could live forever, I imagine that they'd try really hard to find alternatives. I think the main input to whether or not things turn violent is how quickly resources run out after people notice that it's a problem.