Exactly, I find this entire discussion incoherent. Drake Equation can demonstrate that the universe should be teaming with life, or it can also demonstrate that

Exactly, I find this entire discussion incoherent. Drake Equation can demonstrate that the universe should be teaming with life, or it can also demonstrate that we might as well be the only life in the universe: just pick different numbers and no one knows how to pick which numbers to multiply. Until we have more evidence, this is all unconstructive speculation. As a matter of fact, that we can observe the universe and see that it's not teaming with life, is the best argument against assuming the universe is teaming with life. If you were to ask me (and I am a layperson, so you shouldn't) what seems more likely to me is that no matter how large the universe is, life is still rare enough that there is probably no other life in our light cone, which is why our galaxy is not colonized by some other civilization. Of course, we have no evidence to support this, it seems also possible the universe is somehow dense with life but we don't see it for other reasons. It's all speculation.