A very interesting and thought-provoking read.

A couple of thoughts it provoked in me:

First, imagination allows us to suspend disbelief long enough to entertain what might be possible, saving us from failing to invent new technologies simply because we'd otherwise think they're impossible.

Think of flight (Ovid's The Fall of Icarus), submarines (Jules Verne's 20,000 Leagues Under the Sea), travel to the moon (JV's From Earth to the Moon), and many more.

I'd thus hesitate to laugh off anything as impossible just because we don't yet know how to do it. Sure, it may truly be impossible, but it may be possible once we learn more about how the universe works (as opposed to how we currently think it does).

A second thought is that taking the position that there must be intelligent life beyond the Earth (setting aside the notion that intelligent life may not be a good way to describe us humans :)) is currently a great example of exactly the above - something of which we have no proof, but that we're willing to suspend disbelief.

Your argument as to why there has to be such extraterrestrial intelligent life seems to be solely based on statistical arguments with assumptions as to the likelihood of different variables of the Drake equation holding certain values.

That doesn't make you wrong, but it doesn't seem to me to be so much more plausible than there being physics beyond our current understanding that might enable FLT flight one day.

Hopefully, both are right.