Question

the greatest threat to our planet is a belef that some one else will save it

Answer 1

first of all its belief and not belef
and lets try an answer,
yes,it is true that the topic mentioned above is a major threat to our ecosystem as if we do believe that someone else is gonna save our world we do not put in effort form our side 
we are the ones who should make the change and not the people who walk around us 
i end this by saying a quote by mahatma Ghandi 
“Be the change that you wish to see in the world.”