I like how there are different ways to play this game. Camping is godawful misery when done badly, but then so is running and gunning. The abject campers are those who'd rather die where they are than move. Who hasn't seen the Demolisher who puts down their pylon in the LZ on Hydra and refuses to move, and bleeds out (all alone) on every second wave?
But the opposite is possible. Today I had an all-Infiltrator pug game that ended up on Giant and sometime about w4 we all ended up camping the upstairs control room, two up top, two down below. And when we did get overrun, we all split up and kited the enemies elsewhere, then reformed the group either in the ladder room, the LZ, or back in the upper control room. It was pretty enjoyable, especially since all the teamwork was wordless.
This.
Sometimes camping is possible, though in my opinion only when the team coordinates holding chokepoints, which in pugs is possible only with the right combinations of kits, and only in a few places (e.g., giant, hydra's control room, dagger); also, the team needs to be capable of judging when to reinforce one of the holding points, and when to scatter out. As Marksmad mentions, when it happens, it is awesome.
More likely however, camping ends with someone's tunnel vision leading to nasty flank, a chain of revives, someone refusing to use a missile, and a looong game at best, a wipe at worst.
For what is worth, I will try to help a camping team, if they look like they know what they are doing. If not, I might set up a flanking position and snipe all the things while the pugs keep them entertained by dropping to the floor.