As promised I am back with a longer post explaining what I learned from this thread of interesting discussions (after studying and taking a 6 hour sleep). First of all I thank again all the people who explained things so well and enabled me to infer things which otherwise I would have overlooked.

In my first year of engineering I took a course in communication skills. Our second lesson was titled "Barrier to communication" in which we studies what type of inter, intra and organisational barriers are there to communication. I read whatever was written here with an open mind I tried to infer what went wrong in terms of those intra-personal barriers. I found myself guilty on 4 counts of barriers. Let me list them all out.

1)Wrong Assumptions: As I had stated in my original post, I always assumed that internet == public. To me posting something on the internet was like posting it on the bulletin board of the classroom or college. Thus, when all this concern over privacy started I had incongruent thoughts from the privacy aware people.

2)Varied Perceptions: Due to my wrong assumptions, I perceived whatever I read in a very wrong way. It felt like people were suddenly and randomly picking up on something to argue about and hate. This was not so. People had different notions of what to keep to certain circles and what to make entirely public. Thus this barrier further confused me.

3)Differing Backgrounds: Now this is perhaps the most strong and significant barrier that I had. I failed to understand that most of the people who are writing such essays do not have the same cultural background as me. Most of these people were from a developed country and there is certain culture of independentness there. People have different circles of people who are oblivious to each other. But this is not true for me. I grew up in a liberal Indian family. Now a "liberal" Indian family knows everything about each other. And I am not talking just about my nucleus of mother father and sister. I am talking about relations till first cousins. I meet these people every few weeks and they know all about me. Thus everyone in my FB stream knew something or the other about each other and had a actually posted keeping in my that those people would be seeing all this stuff.

4)Impervious categories: I must be ashamed of my self that I fell for this trap, a trap which I like to avoid like a disease. I didn't come in to this discussion with an open mind, I only responded to notions which were congruent with mine. This way I was not able to get to grips to all these thing before.

When I posted this question I had decided keep my mind open and try to understand what happened here. I think I got to grips with most of the problems people have been talking about. Here is a list of what people claim to be the problem with them

1)They do not have total control over there data. So they cannot separate things among groups.

2)Sites like FB violated there trust when they made things public. I read some history and found that when the site was started people joined up so they can share things in private, but now that is very hard to maintain.

This is all I have learned from this brief discussion here. And I again thank you for explaining this to me.