There was never an argument that the 30 second clip shows self defense.

The problem is that Kyle drove out of his way with a non-defensive firearm, with a clear intent to put himself in that situation so he could murder someone.

Let's say I want to experience killing someone without consequences. I leave a nice bike completely unlocked in the bad part of town and hide in the shadows, then when someone tries to steal it, I axe them in the back of the head. I'm clearly a criminal guilty of first degree murder, not a victim of theft.

Unfortunately, I'm not sure how much nuance the American legislative system has for cases like those. Let alone when exposed to the biases our executive/judicial systems have when executing them.