they’re essentially making the argument that if you accept that a civilization can eradicate itself

That’s exactly the “step two” that I’m challenging, though. That’s my entire point. I don’t accept that civilizations like these can eradicate themselves without some further work to establish that.

via nuclear war, climate change, plague, a generation of ipad kids, etc etc

None of those are plausible ways to reliably wipe out an interstellar-capable civilization. Especially bearing in mind that “wiping out” in the Fermi Paradox context requires that they be wiped out such that they can never recover. Full blown permanent and total extinction. Something that merely knocks them back to the stone age is no biggie on the sort of timescales the Fermi Paradox operates on.

I’m pointing out that the “answer to the Fermi Paradox” that these researchers are presenting is incomplete in a very fundamental way. It’s like proposing an explanation for why the Sahara Desert is dry by calculating how frequently you’d need flying saucers to come and steal all the water from it, but not doing any work to establish that there are flying saucers coming to steal all the water. An interesting exercise in playing with probability equations, perhaps, but not a useful one.