Yes, world3 is meant as a simulation exercise that is sometimes taken too seriously. But even its critics consider that the conclusions of the model are valid. Here is the continuation of your quote:
> He does however consider continuous growth in world GDP a problem:
Only the widespread scientific illiteracy and innumeracy—all you need to know in this case is how to execute the equation y=x*e^{rt} prevents most of the people from dismissing the idea of sustainable growth at healthy rates as an oxymoronic stupidity whose pursuit is, unfortunately, infinitely more tragic than comic. After all, even cancerous cells stop growing once they have destroyed the invaded tissues.[7]:338–339
No, lots of critics of the model (like me) consider the conclusions of the model to be invalid. It's inherent in the nature of validity actually - a fraudulent model like World3 cannot be said to be "valid" even if a few of its vague prognostications end up in the right general area. Any definition of validity that allowed such a thing would also have to apply to fortune tellers, who often say things that seem directionally accurate but whose methods are of course not "valid".
> He does however consider continuous growth in world GDP a problem: