Yes, exactly. I think the real reason why we don't see aliens is that once the population reaches certain level of intelligence and awareness, it takes only one generation thinking "this is not worth it" to cause dramatic population collapse which might wipe out entire species. And the thing is, "life isn't worth it" might actually be true, as much as evolution does everything to convince us otherwise.

But now that I think of it, there might be solutions. The problem is, they're incompatible with individualism. Imagine passing a law that everyone is obliged to take care of a child. Sure, this would cause issues, but would instantly solve the population crisis. The problem is, such a law will never be passed in a democratic society, because everyone votes according to what they believe is their own best interest, not the best interest of the group. But an absolute regime could potentially do this.

Now that I think of it, maybe the problem is that human societies grew too big too fast and our brains didn't adapt. We're capable of self-sacrifice, just in a group of max 20, not 20 million. We need a completely new paradigm of organizing the society.