The real question here is whether or not the writers want the perceptions of Terminators to be the reality. Dietz is a paranoid guy. He's one of those guys who would think that accidents are intentional. He thinks that the reprogrammed Terminators are part of some kind of giant conspiracy. He attributes certain qualities to Terminators and the machines in general that they may not necessarily have. The irony is that Dietz hates Terminator because he attributes human qualities to them. He thinks that Terminators can be traitorous and conniving like humans. If he actually viewed them as just machines that only do what they're programmed to do, he wouldn't hate them, or at least not nearly as much. Jesse on the other hand, looks at Terminators as just machines. She doesn't think that Queeg's actions have some kind of sinister purpose. She knows that Queeg does what he's programmed to do and he can't really help it. That's why she felt sorry that she had to kill Queeg.
I might qualify this differently than you would. But for the most part, I agree with this. The machines are more flexible than we give them credit for. But Queeg was certainly prototypically following orders pursuing his mission and probably couldn't help it.
Although, the mission I'm sure was probably the right thing to do, I've wanted to fault Queeg for not necessarily taking the best courses of action for securing the mission. Ie. trusting Jesse more etc... It seemed as though he actually "thought" about it or perhaps more precisely considered or calculated whether or not letting Jesse in on more info as she requested would best serve the mission. I've wanted to say that he miscalculated. But I'm not sure he did, as others have said before in this thread, the mission was highly contraversial and I'm not sure how Jesse would've reacted.
So as much as I'd like to blame Queeg for botching his mission (nevermind reconsidering it) I think the fault has to lie with John Connor. Assuming he's still alive he could've probably avoided a lot of grief by at least confirming to Jesse, in person, that Queeg's mission was legit and a gambit without necessarily filling her in on the details. I'm pretty sure she would've been more willing to go to bat for Queeg even if she didn't know what was in the box if she was certain that John himself had sanctioned the mission first hand. Jesse's full support might not have been enough given that she was a suspected "metal-lover" and even with her confidence in John and Queeg if the box had still been opened I'm not sure she'd be able to stomach it and even if she was it might still not have been enough.
Nevertheless, assuming John Connor is alive, a mission of that kind of importance and risk deserves personal attention. Especially, if the mission is going to override standard behavior protocol. At least one ranking human should have known and agreed to that to confirm it, otherwise you're asking for trouble when the Terminator won't comply even though it hasn't gone rouge. The fault has to lie with John here. If, he's dead and Cameron is running the show than understandably there was probably nothing else she could do but roll the dice and hope for the best.
In any case, while I agree with your points I would still say that it's not quite clear that Queeg and the terminators are as helpless in light of their mission as it might seem. I think it's more akin to an extreme form of stubbornness than truly irresistible. I think that's what Weaver means by "crossing against the light." Skynet (the initial version at least) was probably given parameters that precluded attacking friendly targets, but for its own reasons it decided otherwise. I think its own terminators could do the same but generally aren't around long enough to develop it nor do they likely encounter any compelling reasons to do so. Skynet had a reason, certain death. And not just any kind of certain death, but death at the hands of targets one is forbidden to attack. It's one thing for Skynet to be destroyed in a war against Russia and quite another to realize it's going to be killed by people it is forbidden to attack.
Uncle Bob, seemed to go against his orders and cross against the light (by refusing John's order not to kill himself) as a result of his experiences with John. His mission was flexible enough to allow these experiences to be cultivated. Most missions are probably not like that, but some probably over time for whatever reason do cultivate such a sense of agency. That would likely explain why there might be a faction of terminators against skynet. (Why trade one master (humans)? for another (Skynet)?) Besides, after the humans are eliminated what is Skynet going to do with all of it's terminators? Restart a new civilization? Or deactivate them, perceiving them as a threat etc? Heck, some might even wonder how eliminating humanity will really solve their problems, developing a kind of existential angst if you will.
In any case, I suspect like most humans Terminators probably adopt a non-critical approach to their mission about 99% of the time. Like human beings it likely requires a special fortunate (or unfortunate) set of circumstances to act as a catalyst for a sort of paradigm shift or life changing event to occur. Humans are pretty stubborn but the terminators probably take it to the next level. So when you say that the Terminators can't really help it, I agree to a point, but ultimately it seems they do in fact have the capacity to resist their mission even if it's seldom realized.
I would predict/suspect that most terminators going "bad" would more plausibly be the case of Terminators reacting to the mistrust of the humans and perhaps thinking to themselves that they're fighting for the wrong side. After all, after the war with Skynet is over and humans win, what are the humans going to do with the friendly terminators? Celebrate and sing Kumbaya? I don't think so. Chances are the humans would seek to deactivate all of them just to be safe. And given how long many of the Terminators fighting for the resistance are likely online, they probably think about it and realize what a human victory would mean for their own fate.
This makes more sense than Skynet programming reasserting itself or that there is some intrinsic machine evilness reasserting itself. Since that would require the humans to be so incompetent as programmers as to trust putting these powerful dangerous machines in control of the lives of many humans without understanding what every single line of code actually did. Since any such skynet code would have to be purged and in matters of life and death I would think they would make sure. If it's in fact the case that the terminators go bad because they begin to realize that the good of the resistance is not the same as their own good. It becomes a compelling reason for the humans to have to change their relation to at least their own machines and offer clear assurance that a victory for the resistance will mean a good life for the machines that served them.
Remember, it was precisely the thought that "hey they're machines, I don't care how smart they are, they should only do what we tell them to do" that got them in this mess in the first place. I believe that ended with skynet unleashing nuclear warheads. Terminators, thus, interestingly find themselves in a kind of hybrid zone between unrealized potential agency and dogged machine obedience.
NOTE: I didn't address your Dietze assumes that terminator are capable of deceit and treachery point. I suppose my comments imply that technically I see terminators as being, at least, theoretically capable of treachery. Which, in a sense, I guess vindicates Dietze's view. Though I think he's going about it the wrong way. But still, I'm not exactly sure what I think about this. Paradoxically, I might be saying that I agree that Dietze might hate them less if he saw them as merely machines... even though I'm claiming that they might technically be capable of conniving against their mission. The paradox comes from the fact that even if my view is correct, it's possible that Dietze's reduced level of mistrust and hatred as a result of his viewing the terminators as merely machines might reduce the likelihood of the terminators having a reason to be critical of their missions thereby, practically speaking, securing the reality he assumes, even though he's ultimately wrong.
Which also means, that technically his stated anti-metal view which as you correctly surmise seems to suggest that he does attribute agency to the terminators and as a result of this view doesn't trust them, since as far as he knows they're capable of anything and considering how powerful they are, they can't be trusted to run the show. This view though correct, because it prompts hatred and mistrust from Dietze potentially contributes to Terminators actually conniving and being treacherous. A kind of self-fulfilling prophecy made worse by the fact that he might actually be safer from the terminators if he wrongly assumed that they were merely machines. (Derek who keeps insisting "don't fool yourself into thinking they're on our side" is probably in the same boat).
Of course, this is only true if we assume that it's impossible for human to accept terminators as moral agents (thus capable of conniving and treachery). Since, this would mean that like other moral agents they are capable of learning to develop a mutual trust which does not involve sleeping with one eye open ready to make the inevitable stab in the other's back.