One thing I don't get is that people say leading to a truce leads to the Qunari gaining a foothold on Ferelden, but as the war table missions and Mark of the Assassin seem to indicate they ALREADY have a pretty large one; the alliance just means you get to use it too. So even if you scuttle the alliance you're not denying the Qun a foothold, you're just denying yourself the chance to use it to stop the Venatori.
Also, while the Qunari AREN'T as honorable as they would have you believe, they have no reason to lie in this case - The Venatori threaten them as much as anyone and Tevinter is their enemy so they're not going to prioritize screwing you over killing them. Also, am I the only one who actually sees the benefits of the Qun? We can harp about freedom but chances are we're not jobless shmucks living in the street. Those beggars and whatnot? I'm pretty sure many of them would sign on for the Qun since it gives them a stable job, three meals a day and, if Iron Bull is to be believed, free sex whenever they need it.
I acknowledge the Qun's failures - their treatment of Mages is abhorrent and taking kids away is disgusting - but they have their benefits as well. Freedom for all is good in theory, but in practice less than half succeed and those that don't are trampled underfoot. Solas even cows to it: How many servants go out to be authors? Almost none, but the world wouldn't oppose them....actually, yeah, they would since the rich, powerful and naturally talented would still be picked over the servant.