Facebook's onset of health and normality is going to require some adjustment. It is a frustration for those who study them that there are not enough murderous psychopaths to help isolate, at all reliably, characteristics specific to the type.
Not that this difficulty will ever prevent popular speculation about possible warning signs, now updated for the digital age.
For instance, for those old giveaways "kept himself to himself", "never met your eye" or "had unnaturally pointed canines", now read "was not on Facebook", "had never played FarmVille", "unfamiliar with Spotify".
In particular, given trends in suspicion, the person with no Facebook presence now finds him or herself in much the same position as, going back a bit, a sweaty person who, having lowered his voice in the pharmacy, requested both chloroform and quicklime.
A helpful article in the German newspaper Tagesspiegel has just indicated the risks, for anyone aspiring to mental health, of holding out against Mark Zuckerberg.
Noting that neither James Holmes, the suspected murderer of 12 in a Colorado cinema, nor Anders Behring Breivik was a fan of online social networking, the paper quoted a Hanover psychologist, Christoph Moller, on the implications of Facebook resistance.
"The internet has become a natural part of life," is a translation of his comments which, circling the Facebook-minded world, have prompted a surge of speculation about what wilful withdrawal from that natural life might mean.
For some amateur investigators, Moller's words only confirmed suspicions aroused after the massacre, following internet searches into Holmes' online past or, rather, the outlandish lack of it. On the social media news website Mashable, its editor-in-chief, Lance Ulanoff, said he couldn't "get over what an online ghost Holmes appears to be".
To date, however, Holmes is still unidentified on Facebook and a very natural exultation among its professed addicts, following this confirmation of their superior mental health, has been accompanied, perhaps more surprisingly, by reports that Facebook use is now considered so overwhelmingly the norm that employers are more likely than not to consider documented history of online poking, boasting and friending to be a comforting sign of socialisation and professionalism.
"It's certainly unusual," a US psychologist told CBS of Holmes' online resistance, in an echo of the ostracism that threatens 12-year-old avoiders in a school where everyone else has - prematurely - signed up. Enthusiasts cite a study in which lack of internet use was associated, as much as overuse, with depression.
Contrary to the dronings of Facebook resisters, young people in particular need to anticipate the reaction of a future employer who discovers, with incredulity that gives way only to suspicion and distrust, that an otherwise impressive candidate has recorded nothing online regarding their accumulation of friends, social life or holidays in fun destinations.
This response to eccentricity, together with a human resource operative's inevitable irritation at finding nothing to report, can only increase as the warnings of Facebook sceptics are drowned by internet pundits proclaiming the backward-looking futility of resistance. Even after Facebook experienced slowing revenue growth, a London technology specialist at the law firm Charles Russell shrugged away doubters with: "Everyone is using Facebook. Facebook has become a utility in our daily lives."
For some businesses, not being patronised by an unspeakable mass murderer might not look like much of a plus. Equally, for others, being favourited by tyrants, criminals and the intimates of known killers does not seem to have done much damage. The reputation of Christian Louboutin, for instance, has survived the enthusiastic patronage of the designer's friend, Asma al-Assad. Christian Dior seems equally uncontaminated by pictures of the newbie dictator's wife, North Korea's Ri Sol Ju with her £1000 ($1930) Dior purse. The absence of two leading psychopaths from Facebook appears, however, to be already translating into an uncovenanted, promotional gift to a company that can hardly avoid association with some of the online world's sadder extremes, still visualised by some of us as millions of little Julian Assanges, each immured in the greenish light of a darkened bedroom, wearing socks unchanged for three decades. Smugly, an army of Facebook users now reports that the smelly sock is on the other foot.
Arriving so suddenly after children, in particular, have been routinely counselled to use Facebook infrequently and with enormous caution, thus protecting themselves from - to name some of the more obvious traps - obesity, time-wasting, stalkers, bullying, invasion of privacy, bitching, hideous embarrassment, isolation, career damage and unwitting complicity in Zuckerberg's latest schemes for monetisation, Facebook's onset of health and normality is going to require some adjustment.
Perhaps some of us have been too judgmental in the past about the wholesome exchange of youthful venom and embarrassing pictures. Even scepticism about Facebook's real mission - the commercial exploitation of private human relationships - should perhaps be overlooked, now that the place comes with this guarantee: unpopular with two prominent psychopaths.
Evidence on the back of the above factoid, that young avoiders could soon, if they are not already, be regarded as eccentric "ghosts", loners or privacy fetishists, is a more troubling victory for Zuckerberg. Already, with site after site only available via Facebook membership, the company's unstoppable colonisation of online information is surely more irksome, for a habitual resister, than the alleged social losses of missed birthdays and the addition of long-dead schoolmates to an impressive friends count.
But far from generating significant resistance to a company whose eavesdroppings go beyond anything the News of the World ever dreamed of, this fusion of professional and personal information, along with the relevant advertising, only seems to generate more data-supplying conscripts, in line with Zuckerberg's signature notion of privacy, whereby anyone who prizes it above submission to his social network is not only pretentious, but dodgy. Just what is wrong with reclusives?
"Having two identities for yourself is an example of a lack of integrity," the young moralist informed David Kirkpatrick in The Facebook Effect, a statement yet more uncompromising than Eric Schmidt's to critics of Google: "If you have something you don't want anyone to know, maybe you shouldn't be doing it the first place."
It's three years since Zuckerberg told Kirkpatrick: "The days of you having a different image for your work friends and co-workers and for the other people you know are probably coming to an end pretty quickly."
When people who resist this version of human identity are filed instantly under weird, that end appears to be pretty much here.