We haven’t even discovered all life on earth.
There are life forms on earth that only a few may get to see.
I do agree that “intelligent” life may be exceedingly rare, but then, once life begins, evolution on other planets is in principle no different than on earth.
As Hazen demonstrates, it is all a matter of probability and not a matter of “chance” vs “necessity” and the range of probabilities is rather wide given the enormous spatial richness and enormous time spans.
And most of all, what Kipping glaringly omitted in his lecture is the way abiogenesis actually occurs. He just cited some vague statistics, without addressing the mathematics and mechanics of chemistry → bio-chemistry → life sequencing orders.
