I think you are correct to a certain extent that sometimes being a cunt is useful. But also, I think a the vast majority of times that you are describing “cuntiness” as being useful are not actually instances of being a cunt, and the vast majority of the time, there is no dissonance between being kind and advocating for yourself.

Instead what is happening is that you have social anxiety, with a intrinsic emotional belief that friends or social groups will reject you if you ever cause anyone to feel bad, or annoyed, or bored. And this results in you hiding your thoughts and feelings from others in order to avoid rejection. But what actually happens is that you project Big NPC energy, and people will generally find you to be boring and not worth the effort of interacting with. Or else they will subconsciously notice that you are hiding yourself, and get the intrinsic feeling that you are untrustworthy.

The default belief of the world is that if you want or need something, you need to ask for it. This makes sense - different people have different needs, and trying to anticipate everyone’s every need at all times is time consuming, inefficient, and exhausting. If you are constantly asking someone if they are thirsty, hungry, tired, bored, etc, because you are concerned for their well-being since they don’t know that they should try to anticipate and advocate for their own needs… that is the pattern of behavior you adopt with a child. We expect adults to advocate for their own interest. If the group decides to go to a Chinese restaurant, but you hate Chinese food, then it is your responsibility to say “I don’t wanna eat there - I don’t like Chinese food”. No one wants to try to discern from your subtle facial expressions how you feel about any given restaurant selection. And, again, humans are masters of subconsciously reading people, and if you are consistently wearing an expression of “I’m unhappy about this but need someone else to be the adult and advocate for me” or “My opinion is unimportant and if I express it people will reject me”, then others will read that expression and subconsciously assume the truth of it, and will then treat you accordingly.

And then, for the socially anxious person, cognitive dissonance takes hold. The brain’s top priority is to avoid coming to any conclusion that would require it to do something it considers scary, or difficult, or to change its existing beliefs. And the easiest way to do this is by moralizing. Thus, not speaking up, not expressing thoughts or opinions others might not agree with, never saying anything that might disrupt the social harmony, are things that make you a “good person”. And when other people say things that upset you, or do things you don’t like, or exclude you from things they don’t think you’d be a good fit for, or make plans for things you disagree with, that makes them “bad people”. And since socially anxious people tend to be very self aware, this means they must - as you said - constantly walk on eggshells to avoid becoming a “bad person” by their own definition.

And with this moralizing, the social anxiety has effectively entrenched itself. Since any action, suggestion, opinion, or feeling could potentially make someone upset, and therefore make you a Bad Person, the only moral thing to do is essentially nothing. Never voice an opinion - someone might disagree with it. Never say hello to a stranger - it might make them uncomfortable. Never go for a hug - they might not like physical contact. Never make eye contact - they might not want to talk. Never invite friends to do something - they might have something else to do, or have some objection to it, or you might have to exclude someone. Never tell someone they are pissing you off - your feelings shouldnt make them feel bad. Etc, etc, etc. And so what remains? Showing up (maybe), saying almost nothing, agreeing with almost everything people say, and occasionally voicing an opinion that no one could possibly disagree with, so everyone there will know you are a Good Person.

And while you go about your life, you see everyone else doing all these Bad things now - saying things that might upset others. Asking for pay raises and promotions when others deserve them more. Persuading the group to go to the football game even though not everyone likes football, and the stadium is a waste of taxpayer money. Excluding others from doing cool things, which will make them feel bad. And this makes you feel like almost everyone is a Bad Person, and that the world is terribly unfair, and the only way to get anything you want in life is to do Bad Things. And once again, these feelings of bitterness and unfairness and cynicism and helplessness will unevitably seep into your face, and others will pick up on these emotions and react in kind - seeing that you are an angry, pessimistic misanthrope, and avoiding you, excluding you, or pushing you away, since no one wants to spend time with someone who thinks everyone and everything sucks.

Instead, the social consensus on what makes someone a worthwhile friend or acquaintence is far more balanced. Someone who brings people together, makes people happy, and makes cool, fun, or valuable things happen is going to be more appreciated than someone who simply shows up. And someone who makes social faux pas or sometimes pisses off people is usually easily forgiven - including by the people they offended or pissed off. The default social consensus is that most people are good people, who might sometimes have some flaws, or be a bit abrasive, or say things we disagree with.

The defining feature of a healthy social group is that they believe that most people are good and that mistakes or disagreements are no big deal - and so the most unattractive thing a person can do is believe the opposite. And so, the cycle completes again - social anxiety will make a person a judgemental misanthrope, which will cause them to be rejected by others, which will reinforce their social anxiety, which will reinforce their judgemental misanthropy. And the way to break the cycle is to simply assume that most people are good people who are flawed and make mistakes and have disagreements sometimes, and also assume that you are a good person who is flawed and will make mistakes and will create disagreements sometimes.

Btw, none of the above should be taken as particularly being pointed at any specific individual. These are just trends I’ve noticed among populations of socially anxious people, myself included.