Learned people have been able to convince governments to invest billions of dollars in the search for life elsewhere than Earth.
To me that spells out that they believe there must be life elsewhere. That they believe we are not alone.
Mars devices searching for evidence is a big step. Evidence on Earth indicates just how adaptive and robust the various life forms can be.
Microbes that exist in rock cracks where there has been no rain in 10 years.
Bacteria that lives in deep caves. Existing on alternate energy sources other than the Sun. Or in deep oceans. The number of whole mini worlds of life forms that develop near underwater hot springs. Tube worms etc.
Investigating these weird life forms and the conclusions drawn go to show that scientists believe that Alien life exists. Just because there is no conclusive evidence either way it does not stop them believing it. Possibly they want to believe.
I bet if they were asked, the answer would be, "We don't have any proof either way."
Yet they have the funding to conduct the search. I believe that is a good thing.
Cheers