So, alright, if we want to skip politics, then I'll just respond to:
JC is dead in the future, killed by the robot he adored. There is no hope of avoiding Judgement Day.
Alright, let's look at these things.
The first thing isn't what I'd call dark. We never see it happen, and the premise is one I find proposterous. The T-850 explains that Skynet knew of John's emotional attachment to the T-800 from T2 (no idea how Skynet knows this), and thus deployed the T-850 to kill him. Apparently John's an idiot in the future, because emotional attachment or not, he should be aware of Terminators by now. He should know that this can't be the same T-800. Even in T3 itself, John's first reaction to seeing Arnie is "are you here to kill me?" He does ask about the possibility of T3 Arnie having the same memories as T2 Arnie, but his first reaction is logical. So, no. The "darkness" of the concept is underscored by how future John requires the idiot ball to make it work.
Second thing, no hope of avoiding Judgement Day. Again, it's a premise that undercuts T2, which not only goes against its themes, but literally makes the movie an entire waste of time. In fact, if we factor in Salvation, delaying JD has arguably made things worse in the long run. But that aside, even if JD is inevitable, T1/T2 actually show us the future war. T3 does, technically, but it lacks any of the punch the first two films had.
Also, I feel like touching on this - down to the lighting and cinematography, T1/T2 are much darker films than T3. T1 is brutal when it comes to innocents being killed by the T-800 - the police station sequence might have guns and all that, but it's arguably a moment of horror. T2 doesn't quite have the same level, but what it does have is excellent cinematography and use of lighting, with its use of blues and oranges to add to the atmosphere. By way of comparison, compare the two minigun sequences in the films. The T2 minigun sequence is excellently shot, has excellent atmosphere, and serves as a point of character development for Arnie, in that he could easily kill all the cops there, but doesn't, despite having no qualms about killing earlier on. In contrast, the T3 sequence takes place in daylight, lacks any atmosphere, and lacks any character development. That the T-850 doesn't kill anyone has no deeper meaning because it's not tied to any character development. It's one of the cases where T3 apes a scene from T2, but doesn't take the thematic and character impacts with it.
In short, T1/T2 are dark because the darkness is up there front and centre. Any darkness in T3 is, at best, alluded to.