This is one of "22 virus definitions" (thought-mistakes that cause ineffectiveness and unnecessary negative emotions).
“Humans will destroy the earth.” Not only is this a negative guess, not only is it demoralizing, but it is false hopelessness. It is false in the sense that it contains too much certainty. Nobody knows what will happen in the future. And it is false in the sense that something can be done in the meantime that might change how things turn out.
False hopelessness is a kind of cop out. Like the statement above, it allows you not to try. I hear it all the time. People are convincing themselves of things like this because (at least in part) it absolves them of responsibility. They don’t have to do anything about because “nothing can be done.” But by convincing themselves of false hopelessness, they also demoralize themselves unnecessarily. It takes the fight out of them.
You've heard the phrase, "It took all the fight out of me." One thing many people don't realize is that if you convince yourself of false hopelessness about, say, the future of the human race, that hopeless feeling soaks through and stains your whole life. Your whole body is less energized for accomplishing your personal goals.
If you don't want to work toward ending world hunger, you can make that choice without deciding it cannot be done. You don't have to solve every problem on earth. In fact, you can't. You have to choose your battles. You're reading this right now because you have at least one strong goal. Keep your focus on that goal, and when it is accomplished, put your attention on the next goal.
In the meantime, do not defile your mind with false hopelessness about anything. When you don't know, admit you don't know and move on.
See the complete list of definitions: The 22 Virus Definitions.