Reality programming is mostly for entertainment purposes, and it seems that even the people on the television shows are generally in on the knowledge of this, knowing their personalities may be skewed for entertainment purposes. In most, there isn't much harm in watching, as long as the viewers also know that the programming may not be completely realistic. Economically, television networks have found that reality TV is easier and cheaper to produce than other programming. It may be dumbing down society, though, so networks need to work to make the shows intelligent and with lasting value. Some entertainment shows are even educational, such as The Amazing Race.
Though I personally think that reality television shows are for the most part incredibly stupid, I don't see how they harm anyone more than any other sort of stupid television. The people on them should be well informed and justly compensated, but if they put themselves in that position then it is their decision.