Uhm, I agree with a few people here who say you need to define your terms a little better.
I hear people use "camper" in all sorts of different situations.
For example, there is the person who hides upstairs in Arctic next to the Raptor spawn flinging spider mines down into base. This is incredibly irritating and pretty useless to the his team. Sure you can deal with the guy, but you'll probably lose a few lives doing it. On our server, doing this a lot will get you kicked.
Then there's rolling the tank up onto the brow of hill overlooking spawn and killing people as they appear, or parking a 'Bender on a node and spamming sky-mines as people spawn. This I also think is camping as it doesn't allow people any chance to fight back as they are killed before they even get to the weapon locker. It can be an incredibly successful tactic depending on what stage the game is at. If a team is attacking the final node before making a push for the core, then doing this is going to make it easier for them.
It's allowed in clan-matches as in clan matches the objective is only to win at any cost. On pubs people often forget that this is a game and it's there to have fun. While one person may get a kick and a high kill count from shooting people at spawn, the person being shot is not going to enjoy it at all as it's impossible for them to even get into the game or pick up a weapon, and consequently, this will also get you kicked on our server.
Then there's the "other" camping. This is basically to defend a node. Examples of this would be on the hill next to the tower in Torlan or on the high ground on Crossfire where you can control the final node and kill anyone going to re-take it. I don't think of this as camping as there are many many ways to counter it, you're not killing people who are helpless, they can get the manta (or raptor on Torlan) and attack the tank, also, getting on ground above the tank can make you difficult to kill as you are slightly raised and can rain down flak secondary.
Admittedly, on some maps, you can actually also kill people as they spawn by moving the tank a little (eg: one side of the hill in Torlan) but this leaves you very exposed to LG and SR from th sniper tower and you won't last long.
People who do this are primarily trying to defend to node and thwart counter attacks. Its a tactic which is effective, but also has many counter tactics and so this will not get you banned on a server and for me, doesn't qualify as camping.
Also rolling the tank up behind the final node on Arctic or Crossfire to defend it while your team attack the core. I hear people claim this is camping, but it is merely defending the node.
So for me, spawn-killing when it is being done clearly for kills and doesn't allow for any real counter may be acceptable in clan matches (although I almost never see it happen), but it is lame lame lame in a public server as you are just stopping other people from enjoying the game.
Sabotage? Doesn't bother me at all.