Everything has both positive & negatice aspects. You have seen only the negative aspect. If you see keenly, there are equal number of positive aspects too! Today net is for matured users and sites like orkut can be put behind firewall with password, if one really wants their wards to be away from such sites. These kind of things happen everywhere, not only on net, but also schools and colleges, leave alone other places. You speak on similar lines like that of our social cops, who are determined to ban sex education in schools. It all depends from person to person, that what he or she wants. If you want, you can really have a very clean chit profile with nice flocks in your friend's listing. If you are not comfortable with any particular person in your friend's list, you may always delete him/her as well as his/her scraps. As far as post are concerned, you can always give back if anything is written against you. If you find any community or profile, deleberately against you, then you have the facility to report it as abuse, and repeated reporting of abuse, results in deletion of that profile or community. There are ways and facilities to curb/avoid the things, provided you are ready to accept them! There are much more nasty things happening in and around us in the society!
As I always believe - "When females Tennis game is seen, some prefer to see player's undergarments, while others prefer to watch the actual game, its upto you to decide, what you want to see :-)"
THINK! THINK RATIONALLY!