I'm struck by the assumption in this essay that you have a clear distinction between your own values and other people's.
I think that having a clear sense of personal identity can be difficult and not everyone may be able to hold on to their own perspective. I am concerned that this might be especially hard in an era of social media, when opinions are shared almost as soon as they are formed. Think of a blog/tumblr/fb that consists almost entirely of content copied from other sources: it is nominally a space curated/created by "you", but really it is a lot of other people's thoughts aggregated with very little personal modification. That could be a recipe for really poor internal coherence.
It's pretty standard psychologist's advice to have a journal where you write truly private reflections, shared with literally nobody else. I imagine this helps in constructing a self with boundaries.
Relatedly, "self-affirmation" (really kind of a misnomer: it means writing essays about what values are priorities for you) has a large psychology literature showing lots of good effects, and I find it extremely helpful for my own thoughts. A lot of self-help seems to boil down to "sit down and write reflections on what your priorities are." Complice is this in productivity-app form, The Desire Map is this in book form, etc.
I would respectfully disagree with the notion that "internalized shoulds" as you put them are universally undesirable. I think there is a distinction to be made regarding whether one voluntarily internalizes a new set of values, versus whether those values are forcibly imposed from outside.
For example, I am currently taking up an exercise regimen. One of the ways I motivate myself is by telling myself that I want to be healthy, so I should go exercise. This is opposed to telling myself I should do something because someone else told me to do it.
Another example is that my friend wanted to get good at art. But he was inexperienced, so everything he drew at first sucked. But he kept telling himself that in order to become good he "should" draw every day. In the initial stages, before his art improved to the point that it became its own reward, that internalized should was the only thing keeping him going.
I think that "internalized shoulds" are a stage that every new habit that you're trying to build goes through before it becomes an internal motivation. We shouldn't prematurely cease building habits because we feel that resistance in our own minds.
I tried tabooing "should" from my thinking a few years back, and it went quite well. The worst type of "should" I started to notice is one which I don't think is on that list - it falls on a spectrum between the just world fallacy and the planning fallacy. It's "should" used epistemically.
It comes up a lot in group discussions at work. Examples:
"As long as we <do thing we probably won't actually do>, it should be fine."
"We haven't tested it much, but it should work."
"We followed <unreliable documentation>, so it should work."
In each of these examples, if you substitute "will" or even "will probably" for "should", then the implicit claim sounds a lot more questionable. But "should" shoves off responsibility, makes it feel like its ok to rely on something, because it's not our fault if it's wrong. Even if it's really likely to be wrong.
To me, this form of "epistemic should" doesn't feel like a responsibility-dodge at all. To me, it carries a very specific meaning of a particular warning: "my abstract understanding predicts that X will happen, but there are a thousand and one possible gotchas that could render that abstract understanding inapplicable, and I have no specific concrete experience with this particular case, so I attach low confidence to this prediction; caveat emptor". It is not a shoving off of responsibility, so much as a marker of low confidence, and a warning to everyone not to put their weight down on this prediction.
Of course, if you make such a claim and then proceed to DO put your weight down on the low-confidence prediction without a very explicit decision to gamble in this way, then you really are shoving responsibility under the carpet. But that is not how I have experienced this term being used, either by me or by those around me.
My concern is that there are some share of people who might have internal desires to do harmful things to others and are smart enough to evade consequences, for whom "internalized should not" is the only thing keeping them from doing those things.
I'm not sure that it makes sense, at our current level of knowledge of scrupulosity, to declare that anything is "the" cause of scrupulosity. I have no doubt that what you say is *a* cause of scrupulosity, but the term is deliberately quite broad. For example, clinical OCD can cause scrupulosity, but that's not related to internalized "shoulds", it's related to the mind's tendency to obsessively think about things it's trying not to think about.
Note: This post is about "should" in how people think, in human psychology -- not about "should" in some deeper/broader philosophical sense that might apply to general agents.
I think when people talk about how they "should" do something, there's basically three different types of motivation/shouldness that are meant, and I think noticing this helps make sense of the idea of "getting rid of 'should'" that some people talk about. I'll call the three "external", "internal", and "interalized". (I don't really like this terminology but it's what I've come up with. If you have a suggestion for something better, let me know.)
External here refers to things that are motivated entirely externally -- I don't particularly want to do X, but things will not go well for me if I don't. External "should" has no real moral component to it -- here by "moral" I mean that not in the broad consequentialist sense of what one should do (here by "should" I do mean that in a broader sense rather than a human sense!) but rather that thing that people think of as morality (like for example things that deal with other people's welfare and not one's own, or things being forbidden-or-allowed-or-mandatory).
Internal is the opposite, purely internal -- I feel that X is something that needs to be done and so I am internally motivated to do it. Well, OK -- that description has the problem that it doesn't do enough to distinguish it from the third one, "internalized". I'm hoping the distinction will become clear in a moment when I discuss the third.
Internalized is the nasty one that you want to avoid, the source of scrupulosity, the reason that people talk about "getting rid of 'should'". It's when you take someone else's morality, that you are not allowed to question, and internalize it as binding on yourself. As I said -- this is where scrupulosity comes from; it's not a good thing.
The thing is that if you're not already aware of the distinction it can be hard to describe internal or internalized in a way that couldn't also describe the other. Like, internalized masks itself as internal. Above I said that internal is things that you want to do, that you feel need to be done -- but the person in the grip of scrupulosity would just say, yes, I want to do these things, I feel they need to be done; the obligation is not externally imposed but a result of my own internal desire to do the right thing. Such a person would honestly have trouble recognizing the distinction.
But there is a distinction. The two, well, feel different. Internalized "should" feels, well, bad; it feels like something that oppresses you and gets in your way, even as it's notionally your own internal motivation. Whereas what I'm calling "internal should" doesn't. Another detectable difference, I think, is that internalized should has a certain indirectness to it; it's less "I want to do this thing", as it is "I want to do what is right, and I have concluded that this is what is right". But perhaps that's not the best distinguisher since I guess there are circumstances where internal should can have that indirectness as well.
So when people talk of "getting rid of 'should'", it seems to me they mean "internalized should". Taken literally it doesn't make a lot of sense -- you want to get rid of your motivation? You want to get rid of your notion of right and wrong? But fortunately a person can't actually get rid of their own internal should; but in the attempt to get rid of "should", they can free themselves from their internalized shoulds, from other people's senses of right and wrong that they've tried to incoporate unquestioningly into their own. (External "should" has, as mentioned, no real moral component to it and so isn't relevant here.)
Anyway I think a number of discussions of "should" (again, in the human psychology sense, not in a deeper philosophical sense) make more sense in light of this distinction and the frequent failure to recognize it.