It is true that in the long run, things could work out worse with a guarantee of sufficient food/supplies for everyone. I think, though, that this post answers the wrong question; the question to answer in order to compare consequences is how probable it is to be better or worse, and by what amounts. Showing that it "could" be worse merely answers the question "can I justify holding this belief" rather than the question "what belief should I hold". The potential benefits of a world where people are guaranteed food seem quite high on the face of it, so it is a question well worth asking seriously... or would be if one were in a position to actually do anything about it, anyway.

Prisoners' dilemmas amongst humans with reputation and social pressure effects do not reliably work out with consistent defection, and models of societies (and students*) can easily predict almost any result by varying the factors they model and how they do so, and so contribute very little evidence in the absence of other evidence that they generate accurate predictions.

The only reliable information that I am aware of is that we know that states making such guarantees can exist for multiple generations with no obvious signs of failure, at least with the right starting conditions, because we have such states existing in the world today. The welfare systems of some European countries have worked this way for quite a long time, and while some are doing poorly economically, others are doing comparably well.

I think that it is worth assessing the consequences of deciding to live by the idea of universal availability of supplies, but they are not so straightforwardly likely to be dire as this post suggests, requiring a longer analysis.