re: "Would be pretty arrogant of us, if we thought we was the only living things in this big ol universe........"
If there's life on Mars, then life is INCREDIBLY common.
And if life is incredibly common, then intelligent life is far more common than we thought as well.
And if intelligent life is incredibly common, why isn't SETI detecting it?
The implications are very, very bad for humanity. Within 200 years, humanity will be able to build von Neumann devices that can colonize the entire galaxy. Since no one on any planet in this galaxy has managed to do that yet, the odds are overwhelming that intelligent life is never able to get to that point.
Life on Mars means that the clock is probably ticking on humanity.