What I mean is this. The statements "a large moon makes the axial tilt stable" and "a gas giant greatly reduces how many comets hit small rocky worlds in a solar system" are both verifiable. They are not assumptions.
We also have reasonably compelling evidence that both factors are important for intelligent life to arise. Or, more precisely, good reason to believe that extreme axial tilts and cometary impacts are really, really bad for the biosphere. So the importance of those factors is itself not exactly arbitrary.
You can definitely narrow the Fermi paradox to 'earth-like life' so you can at least attempt to make some sort of estimate. That's reasonable. What's not reasonable is saying this huge assumption is not an assumption. It's totally an assumption, even if it's an assumption you are making because without it, there is even less to say.
There are significantly fewer planets that have gas giants around compared to the ones that don't. It it certain that gas giants prevent debris attacking small rocky planets.
It is obviously an assumption other intelligent life will be like us, we do not know of any other intelligent life to be able to say otherwise. But if I'm looking for life, especially intelligent life, I will look for planets having conditions similar to ours. This is because our sample size is just one, us.
It could be that NOT having gas giants around is how intelligent life ACTUALLY exists in 99.99% of the cases of intelligent life in the milky way galaxy and Earth is the 0.01%. But if I have looked a lot and still just have Earth to guess with, I will continue looking for Earth-like planets. There is no way for me to actually know, but I don't want to waste my time.
There are significantly fewer planets that have gas giants around compared to the ones that don't. It it certain that gas giants prevent debris attacking small rocky planets.
I don't think we know the former and we kind of sort of maybe know the latter for the Solar system right now. As to the rest, I don't follow the relevance, we're not talking about searching for intelligent life at all.
Do you think we're searching for unicellular life then? We're doing our best to search for intelligent life. That means looking for what we know to be able to support life and to eliminate other random searches. Occam's razor and all that. What else are we talking about?
You're right about the former not being certain, but it's definitely rare amongst the planets we've found? And the latter is quite certain.
'planets we've found' is a huge sampling bias because of our current methods. We can't even look for Jupiters, it's unsurprising they are 'rare'.
What else are we talking about?
I mean this thread was not about how we search for life. It's about an estimate of the prevalence of intelligent life - an 'explanation' for the Fermi paradox. I'm saying it's basically a story.
We also have reasonably compelling evidence that both factors are important for intelligent life to arise. Or, more precisely, good reason to believe that extreme axial tilts and cometary impacts are really, really bad for the biosphere. So the importance of those factors is itself not exactly arbitrary.