To me, the simpler explanation is loyalty signaling. A change in behavior represents a change in alliances, so your friends/family are trying to make sure you're not unintentionally signaling your desire to break alliance with them, to join another group. They don't want to lose an ally, or for your nonconforming behavior to negatively affect their status with others within your common social circle.

Isn't this simply another hypothesis? It sounds nice, sure, but I think it would take more evidence than you've given to promote this from plausible to probable.

Btw, in at least some self-help and entrepreneurial circles this phenomenon is well-known, and persons involved in efforts to change or improve themselves are urged to seek out peer groups in which their desired/target behaviors are normal, desirable, and praiseworthy... as well as to expect/be prepared for negative reactions from current peer groups.

This certainly differs from my mom's advice, which is essentially to be a member of at least one "average" peer group, in order to remain grounded in reality. Her idea is that if you abandon your current groups and join some other one, you'll begin to think like them whether their ideas are right or not. Thus, it would be a bad idea to, say, flee Grand Rapids and run off to Santa Clara, where everyone wants to live forever in robot bodies. I might become one of those crazy people.

So, fearing that A is signalling a desire to leave the group, B discourage A's new behaviour; to counteract this, A seeks out a new peer group, increasing the odds that A does end up leaving the group. So B is engaging in classic self-defeating behaviour ... unless, of course, the peer pressure succeeds.

Unfortunately, B's response to A may well be rational, if B expects other Bs to react the same way, leading A to leave the group unless B can make the peer pressure on A to conform strong enough. The various Bs are in something like the prisoner's dilemma with each other; (if I knew my catalogue of game theory better, I'd be able to say just what they're in).

(How did "malice" ever seem like a good explanation in the first place?)

Why not? Are you saying humans are never systematically glad at another's misfortune or loss under certain conditions? I would say humans often are. LWers probably come from societies and situations where this kind of behaviour is less prevalent than the human norm.

In fairness, you did some raise some good points as well, and I'll address those -

The OP describes a phenomenon that everyone knows about.

Indeed. And yet, one many people can't explain. Which is why it's worth thinking about.

The OP then suggests that "stupidity" (a word left undefined) and "malice" aren't good explanations.

I defined stupidity in the post as "impl[ying] poor judgment," meaning going through a conscious faulty thought process. I could have been more explicit about this definition at the expense of pace and brevity, by making the post more heavy and harder for casual readers to digest, without adding significantly more clarity. I suppose it could have been defined explicitly, but I don't think the piece becomes stronger if I do. Rather, I think it becomes weaker for the vast majority of potential readers.

(How did "malice" ever seem like a good explanation in the first place?)

Some of this behavior certainly seems mean-spirited and malicious to people. Many examples available if you honestly can't think of any.

A single word is never a good explanation for an aspect of human psychology.

True, yes, but you must consider audience. There's a reason, unfortunately, why popular magazines are more popular than science journals. Style does matter, which always must be a consideration if you're tackling a complex theme and want your piece to be accessible to a wide variety of people.

The OP then suggests that the "egalitarian instinct" is an explanation. The OP gives little explanation for this explanation,

It has been written about extensively. Again, this wasn't a PhD thesis. In fact, it's been written about extensively here on LessWrong before, notably "Tsuyoku vs. the Egalitarian Instinct" by Eliezer. I suppose I did assume some familiarity with the material that other readers might not have, and could have cited that as relevant prerequisite reading.

no mention of other possible explanations (no acknowledgment of the existence of other possible explanations),

Again, because I was formulating a hypothesis, not writing a thesis.

I appreciate you taking the time to reply and elaborate on your thoughts, but there might be a difference in goals and expectations here. I've attempted to write a series of observations, reason through them, and come up for one explanation for a not-fully-understood phenomenon.

It's already stimulated some good discussion. I'm happy with that result and it has, thus far, done what I intended. I think a longer, weightier, more formal post would have been less effective at the intended goal of putting out observations, a hypothesis, and stimulating some discussion.

Mostly fair points, but you missed the scope of this post. It's a 550 word post that marks a series of observations and a hypothesis.

It has stimulated some good discussion about alternative reasons that this phenomenon exists.

This is not how you go about constructing a model of human psychology.

Your idea of the target scope is off. It was not an attempt to construct a model of human psychology, which would be more fit for a PhD thesis than a 550 word post. It is a series of observation, reasoning, and a hypothesis.

Maybe, but the same kinds of reactions happen even when trying to, say, quit eating donuts.

Heck, there's stories of people from particularly poor backgrounds getting insulted for trying to get a college education. "Don't act weird" might explain radical behavioral shifts, but doesn't explain everything.

I'm a native speaker. "Égalité Irrefléchie" sounds ankward. I preffer "Égalitarisme irréfléchi" (back to male gender by the way). The first would be "thoughtless equality", while my version would be "thoughtless egalitarianism". But frankly, neither sound very good.

We have an approaching idiomatic term however: "Nivellement par le bas". Which quite literally means achieving equality by lowering upper bounds instead of raising the lower ones. It calls the image of cutting mountains off instead of filling the valleys. This expression is widely used as an applause light when talking about schools. (Generally, it goes like: "Let's help failing children in such and such way", then "But that method will slow everyone else down! That's a nivellement par le bas!")

(Oh, and please don't forget the diacritic in Égalitarisme or "Égalité". French typography requires it)

(Also the first E is really É, but one is allowed to omit diacritics on uppercase letters.)

This (allowance to omit) comes from the days of mechanical typewriters, many of which could put accents on lowercase letters but not on uppercase ones. There's really no reason for it now (or ever, in handwriting).

Thanks, amended title accordingly.

To me, stupidity can apply to both types of thoughtlessness as well, but I feel, a moral difference between these two types of stupidity ("stupid" vs. "unreflective"):

If people were being stupid, but knew that their stupidity was causing problems you could condemn them for not being willing to learn more. When people accuse others of being racist, they frequently say "that's ignorant". In this case, ignorance is considered inexcusable. The offender hasn't done their due diligence.

On the other hand, if people aren't even aware that they have some shortcoming that they should be alleviating, i.e. by being unreflective, it's harder to hold them morally accountable. It seems to be normal and perfectly acceptable in modern society not to have ever considered the reasons for your values in the cases that lionhearted brings up (such as junk food, drinking and sleeping).