I don't really consider TF2 a game where you can actually spawn camp. You will always start in your base, and will always have the option then to change characters to one more suiting to killing the guy standing outside. Also, if you are the one camping, it ends up being both good and bad.
Good: because you are cutting off the flow of new enemies that can stand in your way
Bad: because if you are that close to the enemies' base, and you are actually getting away with that much murder, that means your teammates aren't getting the help on the front with capturing points. You are going to fall eventually, and when you do, a whole wave of enemies is going to flood out and rape you and your team.
When I think of spawn camping, I think of when my friends would memorize the spawn pattern in Goldeneye, and run to the next point while the red blood is trickling down my screen form their last kill. There isn't anything you can do then. You will never pick up a better weapon, you will never kill him with your fists, and he will just keep getting points until the game is over.