I graduated from high school the year LTG came out. I was fascinated by the idea and had some programming experience so took on the project of translating the code in Jay Forrester, "World Dynamics" into Fortran and duplicating his results. I would have arguments with my dad in those days about the validity of the whole thing. I would argue that if you did not like some aspect of the model, then suggest something more likely - and we can test out that supposition. My father would argue that there are human factors - our response to conditions, that can't be included in models. We are at the crossroads now. Is humanity able to collectively see our current conundrum and change direction in time, or are we subject to the coefficients in the LTG models?
Since that time the study of complex systems has become an independent discipline of its own. We now know more about the evolution of chaotic systems, about islands of stability, and bifurcation in state space to new uncharted regimes. At the time, the LTG study just said that when the lines on the graphs became too vertical, the models broke down. From the perspectives of complexity theory, this is still the way it is - we just expect that after a period of unpredictable thrashing, the system will come to another quasi-stable equilibrium - that may or may not include a population of human beings.