When they say "They" what exactly do they mean? I have considered many different ideologies, Some of those ideologies aren't entirely popular, So let's gloss over some of that and call it intelligent design, Or even panspermia. To that end What is the origin of life on earth? I'm not speaking about Evolution. Rather, Where did Life and consciousness originate?
Mathematically, To believe Life in this universe is unique to Just here Just Earth. It's improbable at best, and it shows a huge inability to conceive the larger picture of the cosmos at worst. If one subscribes to Intelligent "design" Then Life existed in the cosmos long before we did. Presumably extraterrestrial. Unless a more advanced precursor to bipeds literally existed here and designed us to become what we eventually became.. That's if one believes in religion, And this doesn't negate life elsewhere in the cosmos.
So, Let's assume you align with Panspermia. Life begins with the simplest living organisms that somehow land here from comets and begin to evolve into more and more complex designs because of a necessity, then where did that life come from? What is its origin? And you can't just assume some meaningless germ came to somehow be and evolved Because if it did, This origin wouldn't have occurred just here on this earth, But in countless other places, Or, Maybe people choose to believe that life somehow was scattered all across the cosmos and to spite the infinite time and space the cosmos features, Here, On this tiny spec dirt and water is the only place suitable for life in the entire universe
There are two kinds of people in this scenario, People who want to sell books and people who want to buy them. To believe Life is unique to just here, That we are somehow more special than any other place in the cosmos, Is simply misguided.
There are two basic kinds of believers. The ones who look up at the stars and wonder what's out there, And the ones who look up at the stars and Fear what could be out there...