This is one of the reasons I love this thread! I love how we have different opinions and It's so fascinating to me that you would phrase it as ravings because I wouldn't call his comments ravings at all! I always saw him as a young man who was tortured by a group of people who are very dangerous. He mentions how he can hear noises that are horrible upstairs-from what he has seen, experienced and heard why would he assume any of the mages WEREN'T possessed? He was the last standing Tempar in that section and mages are naturally tempted by demons so their chances of fighting off the evil are probably less good. I always thought he had a really good point. And let's face it-the warden got lucky! They very well could have been possessed and hid it. Cullen's comments were the reflection of years of training and weeks of torture and weren't necessarily wrong. 
I completely agree!
I take back what I said about us being different people. You may write my posts for me from now on!
A couple of things I'd also add to this:
I think it's significant that - as I pointed out recently - Cullen knew the people who were responsible for his torture. These were people he saw every day. People he probably had a rapport with. People he likely never really expected would turn on him even if he was theoretically prepared for it. Being betrayed under those circumstances would make it very, very hard to give people the benefit of the doubt.
Speaking from personal experience for a moment: It is a huge shock when you realize someone you thought you knew has plotted to harm you, even if it's "you" as a group rather than you as an individual. It's one thing if a person snaps and goes after you in anger - that's not that hard to get over. It's quite another to find out someone was coldly planning something even as they smiled to your face. Especially if it's the first time that has happened to you, it really throws your whole worldview for a loop for awhile. It can take a pretty significant level of emotional effort not to let it taint your trust in a whole group of people.
I don't think after being tortured, deprived of food and sleep, probably deprived of lyrium, and having just watched his comrades die a horrible death, Cullen was in any position to exert that much emotional effort. If he had, it would be superhuman, not a realistic expectation. I like that Cullen was only human in that moment.
Also, on a more practical level, judging by the corpses in the tower, Cullen presumably saw mages killing other mages as well as killing templars. It would not be unreasonable to imagine that the mages who actually were innocent were already dead - it would be pretty miraculous for someone who wasn't an abomination or willing to resort to blood magic to be able to stand up to someone who was and live to tell the tale. At that point I... don't think Cullen was very likely to expect a miracle.
One final point on the subject. Cullen's view is seen as extreme only because he was incorrect. If he'd been right and abominations had, say, gone and slaughtered a village as a result of the decision to spare the Circle, would we see it the same way? Because that very easily could have happened. Either decision ould condemn innocent people to death.
I think this is more a function of the Warden being insanely lucky than Cullen being objectively in the wrong, truth be told.