If anything life as we know it is a very low probability process due to many filters that we were somehow lucky enough to pass. Some of them for sure we still don't even realize yet.
Life being plentiful in the universe, and the kind of lame arguments for this assumption, entered into the secular science enthusiast dogma as a countercultural reaction to the prevailing Christian dogma of life on Earth being special. Sagan/etc's hand-wavy argument about the number of stars being a prime example.
The dogma is such that people who subscribe to it will often reflexively assume that anybody challenging it is a disingenuous Christian. FWIW I am not a Christian, nor do I have any other religion, but I think there is fair reason to doubt that advanced life is common. For one, you don't have to stack too many improbabilities to easily overpower the number of stars. Secondly, evolution isn't a process that works towards the goal of creating human-like advanced life; in fact if anything it favors crabs a lot more than smart apes. Third, and most important, the rare earth hypothesis is consistent with all of our observations thus far.
> fair reason to doubt that advanced life is common
Emphasis mine. This is an enormously different and stronger claim than just "life is common". Personally I think it's most likely that cells are relatively common (given a habitable planet anyway), but anything as complex as a fish is very rare.
I think it's reasonably likely (but not certain) that simple forms of life are plentiful, and it is even possible that life more advanced than us exists out there. What I absolutely reject is the notion that I should feel quite certain of the latter because "so many stars!"
Counter: the [Robin] Hansonian universe.
('Grabby Aliens' in his unfortunately chosen IMO nomenclature). However rare life is, and however rarer intelligent life is, it expands to fill galaxies, even allowing for lightspeed limitation.
A century ago or so, it was popularly thought that Mars was covered with irrigation canals, obviously created by some advanced form of life. That was debunked and the hope shifted to maybe there being some fungus or plants... Such were not found so it shifted to microscopic bacteria. There is perhaps some evidence of those, but nothing conclusive, so now people are talking about cracking open rocks to find the fossils of bacteria...
This all has an uncanny resemblance to the "god of the gaps" phenomenon. As science explains more of our world, the religious cram their gods into smaller and smaller gaps in our scientific understanding. And as science shines light on the apparent sterility of Mars, alien life enthusiasts cram their proposed aliens into the ever smaller gaps in our knowledge of Mars.
Oh, life being common is an older idea than that. In the 1700s it was common belief that each of the other planets in our Solar System was inhabited, because otherwise their existence would be a waste, and because of vulgar Copernicanism.
People can expect that life is common any amount they like (well, if they stay within the 1 in a few thousand planets upper bound we have as a fact nowadays).
My problem is with people insisting that's a certainty.
I'm pointing out that common belief was hilariously wrong in the past, so there's no reason to think it's not hilariously wrong now. The meme that "there's lots and lots of stars, so life must be out there" is not sound reasoning.
That's a really bad take that just won't die. Life being a fast, high probability process is one between quite a handful of explanations that fit it.
But anyway, adding Mars and the asteroids into the equation doesn't radically change the numbers.