I spawn kill to keep assets on the ground. For example, Gulf of Oman. If I'm on the MEC side, I'll jump in the bomber, and bomb the ever-loving crap out of the carrier. BUT, I only bomb the vehicles. This is to say that if you're there when I come screaming down, you're just a casualty. I'm after the other jets and the choppers. It helps my team from dying by their hand.
Now, if you go to a spawn point, specifically to stay there and kill people when they spawn, then you're a piece of shit fuckstick mother-fucker that needs to get anal-raped by a silverback gorilla. You're a worthless cock-sucking fag-whore, that needs to cleanse yourself from the world's gene pool. Put simply, take a gun to your head and pull the flippin' trigger.
The only exception I feel, is if your team owns every flag on the map, except for the uncappable one(s). Then it's a free-for-all until the round ends. But, if you sit at a cappable picking guys off as they spawn, then read my previous paragraph.
