In Eccl 9, the topic isn't the second death, or eternal things (do people have the same eternal fate? no, he's talking about our temporal lives)... the point of Eccl 9 is that while you're here on earth you have this certainty of death that should motivate you to do all you can do while you're still alive. The dead don't have the certainty that they will die, because they are already dead. It's not that the dead "literally know-not-anything", but it's that they don't make these considerations like living people do. Their opportunity to contribute to this life is gone.
(You can see in the scriptures where "anything" is used in a non-literal way...
Amnon was sick with frustration over his sister Tamar, for she was a virgin, and it seemed implausible for him to do anything to her.
Now, if you know the story, you know that he is not upset because he can't take his sister out for a walk, or take her to a movie. The "anything" he want's to do to her is actually quite specific.)
With 1Cor15, in verse 27 Paul even makes mention that words that seem absolute (like "every" or "all") can have implied exceptions . Sometimes they mean "every" or "all" of an implied subject. So, "every tear" being washed away, and God being "all in all"; when the scriptures say these things it is obvious that he is not talking about people in the lake of fire. So, this isn't really a good verse to use to support annihlationism either.
The fact that God never considered asking people for arbitrary human-sacrifices has nothing to do with his final judgements and the lake of fire, so I thought it was weird for that to have even been brought up.
I think it is sufficient for me to say that whether "forever and ever" means "eternally" or "a really long time"... being in a lake of fire for any duration probably sucks to the extent that it is not a place you want to go. But at the same time, what I take away from the bible is that the people that are thrown into the lake of fire would actually rather be there than with God anyway. If they were given a choice between "God" and "Lake of Fire" they would choose "lake of fire", regardless of whether it was a place of anihlation or eternal torment.
I tend to agree that annihlation doesn't quite inspire 'fear of the lord' like eternal torment does. Professional athiests seem to readily accept non-existence; so, I tend to think that annhilationism is one of the lies that non-believers use to wall themselves off from God.
Professional athiests, and i've noticed some "jews" are really, really appalled by the idea of eternal torment; and when Christians seem to be appalled by it, I can never get behind their reasoning as to why it is so appalling, and it is somewhat alarming.
At the end of the day, though, I don't think we are responsible to understand precisely what occurs in the lake of fire; because it's a "god's judgement" sort of thing- like, because we have limited human capacity, we can't understand everything he does. Wrath is his, and he will repay- that's what he says- how he does his wrath is beyond my ability to assess, we can't see what he sees, so we can only trust that whatever he does is the righteous thing.