I'm not sure what you're referring to with decoys and shields, which I'll just leave at that.
My hypothesis is that reasoning as we know it evolved as a mechanism to both persuade others, and to defend against being persuaded by others.
Consider priming, which works as long as you're not aware of it and therefore defending against it. But it makes no sense to evolve a mechanism to avoid being primed, unless the priming mechanism were being exploited by our tribe-mates. (After all, they're the only ones besides us with the language skill to trigger it.)
In other words, once we evolved language, we became more gullible, because we were now verbally suggestible. This would then have resulted in an arms race of intelligence to both persuade, and defend against persuasion, with tribal status and resources as the prize.
And once we evolved to the point of being able to defend ourselves against any belief-change we're determined to avoid, the prize would've become being able to convince neutral bystanders who didn't already have something at stake.
The system 1/2 distinctions cataloged by Stanovich & West don't quite match my own observation, in that I consider any abstract processing to be system 2, whether it's good reasoning or fallacious, and whether it's cached or a work-in-progress. (Cached S2 reasoning isn't demanding of brainpower, and in fact can be easily parroted back in many forms once an appropriate argument has been heard, without the user ever needing to figure it out for themselves.)
In my view, the primary functional purpose of human of reasoning is to persuade or prevent persuasion, with other uses being an extra bonus. So in this view, using system 2 for truly rational thought is actually an abuse of the system... which would explain why it's so demanding of cognitive capacity, compared to using it as a generator of confabulation and rhetoric. And it also explains why it requires so much learning to use properly: it's not what the hardware was put there for.
The S&W model is IMO a bit biased by the desire to find "normative" reasoning (i.e., correct reasoning) in the brain, even though there's really no evolutionary reason for us to have truly rational thought or to be particularly open-minded. In fact, there's every evolutionary reason for us to not be persuadable whenever we have something at stake, and to not reason things out in a truly fair or logical manner.
Hence, some of the attributes they give system 2 are (in my view) attributes of learned reasoning running on top of system 2 in real time, rather than native attributes of system 2 itself, or reflective of cached system 2 thinking.
Anyway, IAWYC re: the rest, I just wanted to clarify this particular bit.
Actually, system one can handle a surprising amount of abstraction; I don't have one handy, but any comprehensive description of conceptual synesthesia should do a good job of explaining it. (I'm significantly enough conceptually synesthetic that I don't need it explained, and have never actually needed an especially good reference before.)
The fact that I can literally see that the concept 'deserve X' depends on the emotional version of the concept 'should do X', because the pattern for one contains the pattern for the other, makes it very clear to me that...
A currently existing social norm basically says that everyone has the right to an opinion on anything, no matter how little they happen to know about the subject.
But what if we had a social norm saying that by default, people do not have the right to an opinion on anything? To earn such a right, they ought to have familiarized themselves on the topic. The familiarization wouldn't necessarily have to be anything very deep, but on the topic of e.g. controversial political issues, they'd have to have read at least a few books' worth of material discussing the question (preferrably material from both sides of the political fence). In scientific questions where one needed more advanced knowledge, you ought to at least have studied the field somewhat. Extensive personal experience on a subject would also be a way to become qualified, even if you hadn't studied the issue academically.
The purpose of this would be to enforce epistemic hygiene. Conversations on things such as public policy are frequently overwhelmed by loud declarations of opinion from people who, quite honestly, don't know anything on the subject they have a strong opinion on. If we had in place a social norm demanding an adequate amount of background knowledge on the topic before anyone voiced an opinion they expected to be taken seriously, the signal/noise ratio might be somewhat improved. This kind of a social norm does seem to already be somewhat in place in many scientific communities, but it'd do good to spread it to the general public.
At the same time, there are several caveats. As I am myself a strong advocate on freedom of speech, I find it important to note that this must remain a *social* norm, not a government-advocated one or anything that is in any way codified into law. Also, the standards must not be set *too* high - even amateurs should be able to engage in the conversation, provided that they know at least the basics. Likewise, one must be careful that the principle isn't abused, with "you don't have a right to have an opinion on this" being a generic argument used to dismiss any opposing claims.