I am using the assumption that some people have used by saying given there are billions of stars/solar systems by probability there are a fair few similar to our own with a planet similar to our own, at the right distance from their 'sun' composed of the right materials to sustain life, and also be of a gravitational pull able to sustain an atmopshere and hence life. If there are indeed thousands of these - which you now use the laws of probablity to base this assumption on, you would also think that these life sustaining environments are at different stages of development. Given the age of the universe, some might have been extinct, some less advanced than us, and some more advanced. The other assumption is they believe like us, that there is life out there, and have attempted to make contact - yet there is no sig of this contact.
In fact, correct me if I am wrong, I don't think atronomers have found a planet like earth in the universe yet - at the right position to be able to sustain life.
What is unique about Earth is not only it's position from the sun, but it's size (and hence its gravitational pull) and its composition.
While it is not unfeasible that similar planets could exist, I think it is highly improbable