I broadly agree with your point vis. the problem of requiring employment to gain access to food, but the real picture seems to be more complicated. In game-theoretic terms, once supply outpaces demand, demand often expands to fill available supply. If we can afford to provide food (or, more generally, energy and a small amount of material resources) to everyone simply by virtue of their existing, and we don't provide any controls over the level of population, it's only natural for population to balloon to fill up supply so that we again arrive at an equilibrium where we can't afford to feed everyone.

Broadly speaking, the argument for overpopulation is that population must be kept at a fixed level below the maximum carrying capacity of the environment, if everyone is to live comfortably.