There's no paradox, there's just people plugging in guesses for numbers which almost certainly wildly exaggerate the likelihood of intelligent life arising.

It took evolution 75% of its available runtime to produce intelligent life (which itself was likely the product of a particular runaway process which has happened exactly once on this planet), with a number of near-misses that would probably stagger the imagination if we knew about them all (indeed, the few near-misses we do know about -do- stagger the imagination, and lead people to believe religion might have something to it after all).