It's a legitimate tactic to win.
But it also depends on what game your playing too. Camping in more "arcade style" games, if you will, like CoD is usually a richard move but I don't see a problem if you are defend and objective.
In Battlefield's Rush or Conquest modes or Planetside 2, if your bitching about camping, especially when you're the one who's assaulting something then your pretty much handicapped because that is the most effective way to hold an objective.