[[Nice argument, but unfortunately it isn’t true. There are living creatures whose blood clotting works just fine without fibrinogen.]]
Not sure what your point is? fibrinogen is missing in a certain species? Big deal? Again, how does this relate to humans or species that rely on fibrinogen? Have they shown the species that doesn’t need it had it in the past, but lost it without ill effect? Have they some other mechanism/system that precluddes them from needing it like the vast majority of species do? If so, this argues against IC how? It doesn’t- and you know it- IF you or any other critic of Behe can show that species that doesn’t need it doesn’t have any other species specific system, and that common descent is fact, and that that species lost the need for Fibrinogen at some point, then and only then woudl you have a case that human and the vast majority of species blod clotting system isn’t IC- but as you full well know- that species could very well have been created with different mechanisms at play than most other species- Do we see the need for Fibronigen arising in other species down through time? You coutner argument is weak.
No one in biology claims you can simply knock out a key gene in a modern organism without consequense. And no one claims that there are humans with working blood clotting systems that work without fibrinogen.
What evolution claims is that there can be simpler versions of systems that have function. Not necessarily even the same function. Just function.
In this case a simpler version has the same function. The system that Behe -- on his second go round -- said was irreducible, is in fact, reducible.