Here's the problem...
He wants to kill you. He wants to cut off your left hand and kill you.
And He is so arrogant he does not want to even talk to you.
He sees you as an ant and will kill you like one.
So.....That plan is a no go.
Why not just let us not resist him, then? That wouldn't take too many resources.
That sounds cool and original, we've never done that before
*sarcasm*
Actually, we were able to do it in DA2 and DA:I. Though in the end Hawke's choice didn't matter and DA:I's was a bit more implicit.
Of course they do! They are not total savages. Have you seen Cory's long claws? Yeah, that guy regularly gets a manicure.
I thought he was sealed away... When would he have taken the time? Who would have done it?
At the very least we should be given the option to attempt to join him by asking (causing massive disapproval with our companions
)
What bothers me more is why we cant use the anchor to attempt to enter the black city ourselves.
That would be great! And I suppose it's to keep the religion vague.
For the same reasons you cannot ally with the Reapers in Mass Effect, cannot ally with the Darkspawn in DA:O, cannot ally with The Mother in DA:A, and cannot ally with the Qunari/Arishok in DA2 (... notice a trend here?)
A lack of positive interaction with our antagonist? Why is violence always the answer? I'm starting to see what the critics mean about video games influencing people negatively.
You're a tool to be discarded after he's done with you.
Oh, and he'll also cut off your hand and hang it to a chain that he'll wear around his neck. Or his hips if he makes one side cut to his robe. Those socks and heels.
That'd be a proper ending. I'd take that over the nothing we have. I'd even fully expect it.
Considering Inquisition isn't the last chapter of the story and we're still going back to the DA world in future installments, being able to side with the guy who wants to radically alter the world would be a bad idea from a long term narrative perspective. The next game would just end up retconing that ending anyways.
What's wrong with having a non-canon route? Like Darkspawn Chronicles? Or Anderson as councilor? Plus Bio has already shown a willingness to disregard player choice and do what they like. I don't see why they can't allow us a few more freedoms interacting win our antagonist in meaningful and unexpected ways.

I've said it before, I'll say it again, and I'll say it till the day I off myself, I am not being facetious.
Also, why can't we romance Corypheus? Bioware has always been about inclusiveness and open-minded romance options. Who's to say that my Qunari mage can't develop an interest in the thousand-year-old darkspawn magister trying to kill her and take over the world? Grow up, Bioware. Get with the times.
That sounds great! I'd love to see what Bioware would do with a romance of a... Whatever Darkspawn are antagonist. It'd give us something unique!