Becareful, you'll bring up a big argument about global warming!
The purpose of that speech titled "Aliens Cause Global Warming" was to denigrate proponents of global warming. Crichton also ridicules the idea of nuclear winter. Sagan attracted lots of critics because of his liberal politics.
I'm only talking about Sagan's work on Astrobiology. My view is that biology will be found to be universal on planets and moons in the Solar System, either on the surface or subsurface.
On that basis, my view is that he'll be regarded as the "Father" of Astrobiology.
Of course, if you have no interest in the idea of life on other planets in our system, you'll have no regard for his work in Astrobiology.
Bob Clark