Sorry, I don't buy it. I still see it as (a) map dependent, but (b) still generally a pretty lameass tactic.
It depends on HOW it happens, though and what the exit looks like. If the exit's got plenty of cover for exiting troops, if there's not a long clear line of sight to it for the enemy, I've got a lot less of a problem. Also, if a squad leader's there and can smoke the exit to cover the troops, less of a problem.
But, if it's a fish-in-a-barrel situation, I don't care how much it's the other team's "fault". You're still showing zero consideration for them as gamers, and frankly I think that's a bunch of crap.
Plus, what kind of challenge is it to shoot people as they come out of the spawn and can't even see you? As a person on the team of the exit camper, I usually am getting pissed because there's nothing for me to do while this exit camper just sits there and hoses the team down.
Like I said, if the map's designed well it isn't usually a problem, but generally speaking locking a team up in to their spawn is just boring to me and isn't a sign of any real challenge.
But then, I don't like to play a round where my team "Totally pwnz" the other team. I don't like Superbowls where one team CLEARLY dominates the other team. I find that all intensely boring. I much prefer a tougher fight, like one that comes down to literally the last minute, where both sides are unsure of the outcome. THAT, to me, is a "gg", not some "HAHA!!! My team kicked your team's ass!" game. Especially if that was accomplished with exit camping, it doesn't impress me any.
This has, however, been a longstanding debate in the online gaming community. There are some gamers who are more concerned with winning than with the fun of the game. I like both, personally. I like to win, but I like to win on a map where the enemy gave me a real challenge. I don't like bullying kindergarteners or pulling the wings off flies.