There are more things in Heaven and Earth than are dreamt of in your philosophy.

Every single world in the Solar System is different from the others.

Every single star in the Galaxy is different from the others.

Every single star system is different from the others.

Every single exoplanet is different from the others.

We are looking for an Earthlike world around a sunlike star in a habitable zone orbit.
We might find one but very soon after, we'll discover how different it actually is.

We don't know what level of similarity it must reach to really become interesting.
We didn't know when Viking was sent to Mars that life on another planet would require searching for things that needed to be different from what we knew on our planet.

We are very limited in our knowledge of what's out there. We know practically nothing. We doubt.
But that's not important. What matters is searching.