The banter you posted works in my favor. According to it, the mages who remain alive in Redcliff are thus either willing to serve Tevinter or just too scared to run.
Which is understandable; as least in regards to the second group; but not praiseworthy.
No it doesn't, because it's referencing an event that hasn't happened yet by the time you reach Redcliffe, and doesn't happen at all if you choose to do In Hushed Whispers.
Again, you're trying to make a statement no less asinine than "Clearly, all those who remain at Therinfal are there because they have no problems with corrupted Lyrium or serving ancient Magisters".
So, what you mean is that we really don't know why Fiona was imprisoned. It could have been for any reason, not necessarily an heroic or selfless one.
There's not a single person in that prison that was placed there for anything else.