Another contra-argument is the extreme unlikelihood that complex creatures on another planet with a totally different evolutionary history would in any way resemble complex creatures on Earth.
Why is that extremely unlikely?
I would find it more likely than not, if said life was on Mars.
The closest planet to Earth's specifications in our solar system, and only one planetary hop from Earth.
Sure, if you're talking interstellar life, yeah, way different, but Earth and Mars share material.
Meteoritic material from Mars makes it's way to Earth, and vice versa.
Past mega impacts, have undoubtedly shared material between these two celestial bodies.
(Chicxulub impact would have been able to put a mountain into orbit, no doubt some Earth material made it to Mars, and that wasn't that long ago. Who knows what ancient impacts of the past were capable of.)
Besides, life on Earth evolved as it has, because of advantages over hundreds of millions of years. Over a long enough time span, wouldn't all creatures approach similar advantages, with a similar over-arching specification.
"In a Universe with gravity. On a planet with a central sun. Same base elements and periodic table. etc..."
You would really have to prove to me, that there is some magical difference between life on planets... When we only have one data set.
I'm not making a sweeping generalization. I'm making observations based on our only data set.