The way I see spawnkills:
If they're in my spawn: I shouldn't have let them into my spawn in the first place. If I want to stop it, I should stay alive so I can go and clear it out when my teammates report trouble, instead of dying and letting myself become vulnerable. You're always responsible for your own deaths, no matter how long the cause and effect chain is. Even if they throw a grenade halfway across the map and it blows up in your face, it's still your fault for standing in a place where grenades fall! Chess players don't complain when they lose because they didn't see it coming, they realize they should have planned for that contingency.
If I reach their spawn: They have to deal with me. That's the point. They will have fewer people to attack objectives, and fewer to defend objectives, because they left a hole open in their lines. It's their fault for dying, not mine. I didn't plow my way over there just so I can stop and say "Ooooops, sorry I got so far into your territory, I'll take a few steps back and run around in the open so you can come out and shoot at me." The enemy can 1) Bring people off the front line to deal with me 2) Invade my territory so that I need to go and deal with it 3) Keep trying to kill me as they spawn in 4) Lose as a consequence of their inadequate defense.