Perhaps unsurprisingly, younger Internet users are more likely to regret some dumb-ass thing they did online, with 24% of users under the age of 45 saying they had "engaged in regrettable actions," compared to just 13% of poll respondents ages 45+. Interestingly, men are more likely than women to regret some part of their online past (21% for men versus 15% for women).
The really remarkable findings, however, reveal widespread reservations about social media's impact on personal life. Fully 51% of adults surveyed by Marist said they think that social media does more harm than good when it comes to personal relationships, compared to 29% who think the overall effect is positive (20% are unsure). On this point men and women were in perfect agreement, with 51% of respondents of both genders saying social media does more harm than good.
All of which begs the question: why do people use social media then? My guess is idle curiosity, leading to endless profile surfing and the casual (or more serious) flirtation, which sometimes results. I also think people who subconsciously want out of their current relationships may use social media to precipitate the crises that force their partners to dump them; this way they get what they want without having to take responsibility or admit their lack of commitment.
As for genuine regrets, all I can say is it's actually pretty easy to avoid doing something stupid online. Here are some good guidelines: 1) no naked pictures or lewd talk; 2) no pictures or discussion of illegal activity; 3) no offensive language, e.g. racist, sexist, homophobic, etc.; 4) no posting or sending anything while under the influence. Anyone have any other rules that we should add to this list?
I recommend Clay Shirky's Cognitive Surplus for a better thought out explanation on why we use social media. Your best guesses of curiosity and a subconscious need for self-destruction are pretty low on my list.
Higher on the list: Affirmation, Connectedness, Procrastination, Self-promotion, Entertainment/curiosity, and Information.
I think the self destructive part you note is neither intentional nor subconscious -- it is likely due to the seeming intimacy of the medium, combined with its unprecedented reach and permanence.
If you walked into your workplace or school in your underwear -- you might quickly feel self-conscious because of the reactions it would elicit. But you might feel perfectly comfortable in your underwear in your home. And if you posted pictures of yourself in your underwear (seeking affirmation) you might never feel self-conscious about it unless someone pointed out that you probably should.
I believe that people have an assumption of privacy in their personal lives that doesn't extend to social media, where everything you post can be seen by many, saved to come back to haunt you, or commented on by individuals you don't know. It's rather like finding you're standing a street corner of your home town in your underwear, and not really knowing how you got there. As a society, we are perhaps used to several decades of "anything goes" and not having to explain ourselves or our actions to others. Suddenly, everything you say and do can be held up for public scrutiny and personal accountability.
Perhaps the need for prudence, discernment, accountability and civility catches many people off-guard.
I find it surprising that social media is having zero effect on the debt ceiling impasse and debate. No matter how many people ask you to retweet your rage at congress and update your Facebook status with angry sentences and phrases, no one in congress appears to be paying attention or really caring. Social media and its ineffectiveness is another real loser in this issue.
http://mankabros.com/blogs/onmedea/2011/07/26/debt-ceiling-impasse-1-social-media-0/
I agree with your list of what NOT to do online. However, here's another one that is quite subtle...
Avoid "complaining" - which makes you look like a negative and grumpy person. I have certain friends who do it quite often online - and it's getting tiresome. And face it, who wants to be friends with, or do business with someone who has a poor attitude.