Philosophers going back to Plato have argued that man is a social animal. In more modern terms, that human beings are not solo units, but rather an element of a social set (to use some mathspeak that fits well here).
So many people, it seems, pride themselves on their individuality and claims to being an individual with little or no ties to anyone else, and no dependence on anyone else.
This is a bunch of bunk, to phrase it politely. There are good aspects to being an individual and having an identity that distinguishes you from those around you. Where it begins to go wrong is when it becomes the idea that not only should you distinguish yourself from those around you, but the less you depend on them, the better, and if you could not depend on them at all and be perfectly alone, that would be the best.
Of course, this isn't clearly reasoned out by most people, but this is a summation and analysis of what they would say if they expressed their feelings and proto-ideals into clear and reasoned concrete words.
As a human being, one depends on other human beings. Not only for the physical resources they provide (if we all had to hunt for our food and print our own books and smelt the copper ore needed to make wires rather than have other people that specialize in these things provide them to us in exchange for something, we'd still be in the stone age), but for the psychological component.
As funny as it may seem to people, the human thought process is very fluid and changing, not a process set in stone like that of computers. Away from other human beings that serve as a sanity-check, human thoughts tend to go in odd, un-productive and un-healthy directions. This can be summed up as the 'weird hillfolk' principle - with increased isolation from human society, the less sane human thought becomes.
Sane, in this aspect is an expression of mental health in that ones actions stem from a basis of logical thought. In other words, one does something this way because it is what works the best. When one starts to do actions that don't stem from a logically sound basis in thought - making all the tables in one's house aligned in respect to magnetic north in order to make one's food taste better - society allows for there to be a sanity-check on these actions.
One's neighbor might said "That is really rather silly and doesn't work" or any other member of society may serve as a sanity-check. This is a good thing.
The more isolated and cut-off from human society one becomes, the less checks on sanity there are. This is a bad thing.
The internet is often offered as a recourse of those who prefer to interface with society on their own terms without having to deal with the negative aspects of being immersed in it - like putting up with one's neighbors.
However, the internet is a poor recourse at best as a substitute that serves the same function as society at large in keeping one sane. This has to do with the selective aspect of it - one can pick and choose that which one wishes and does not wish to see. Also, the internet only shows that about one which one wishes to display, disabling the ability to have a comprehensive sanity check. This selectiveness can allow for non-sane / non-healthy thought process to grow unchecked in their influence on one's mind.
In plain English, you get to pick and choose what you see and don't see, who you interact with and who you don't, and what other people see about you and what they don't. The selective aspect of this gives rise to the ability of un-sound thought processes to grow unchecked in the aspects of yourself that you don't display to others. As far as the other people on the internet can tell, you are a completely normal human being. Except for your obsession with eating your own hair. But you don't choose to display that behavior to others, so they have no idea that it exists. This is a bad thing.
More or less, this serves for an argument in support of human beings as social creatures and against the argument for human beings as individuals in complete isolation from those around them.
