They don't look ahead and say, oh, wait a minute, if we do this we will shortly be overcrowded and fall to killing each other. No, they live in the moment, eat and breed and then fight and die. Other animals do the same thing. The earth is a cage, we don't see any way to get off in great numbers. The rate of food production is finite.
Population continues to grow.
That is a recipe for a die off, and you sit there, and say that there is not enough evidence. Get me the technology first, that springs us out of this trap, before you go telling people it might be ok to bet their lives on it. Eyes firmly shut, forward, march. This is a good statement of an essential problem. We have plenty of very solid science, no one wants to hear it.