Is it "justifiable" to shoot someone if I feel I'm in danger?

Yes, but it's a little "shakie". But people feel like they're in danger for alot of reasons; strangers, prostate exams, etc. If you're walking and someone says "hi", you wouldn't shoot them because you couldn't trust them! On the other hand, it'd be a different story if they came up to you and started beating you up, and you were at the point of being killed. Then you'd use the gun! That's self-diffence. Since these bikers didn't do anything to you, I don't see why you'd need to shoot them, and end there lives.