The 'bad guy' is whoever is the aggressor. Everyone has a right to life; if someone starts shooting at you, or swinging a bat at you, you have the right to defend yourself, and if you kill the aggressor in self-defence, so be it.
I've heard from an internet lawyer that it's possible in principle for two people attacking each other to both have grounds for self-defence, too, if both were in reasonable fear for their lives. Whether A kills B, or B kills A, either may be able to argue self-defence given the right (wrong) circumstances. But that's just some internet theorycrafting I heard.
It's a cognitive trick used to assign a label. All you need is a frame of mind, a professed sincere belief and it's done.
Most wars of aggression were sold as self defense.
Jonathan Swift even poked fun of this in the 1700s. It's a really old trick.
The problem is some people get extended the credulity of self defense and others aren't.
Could I declare self defense against a police officer?
Why not?
Aren't they just another human susceptible to the same emotions and aggressions?
They are always given the benefit, a priori, regardless of circumstances, carte blanche, every time. Even in a mere theoretical framing, police are immediately assigned the "self defense" role. It could be over the death of a child playing in the front yard or a family dog, doesn't manner, apparently justified self defense every time.
That's exactly this dynamic at play again. It gets used in the writings of gruesome mass shooters. They were forced to kill all those people to defend some amorphous idea, the country or the race or some thing.
Self defense is a valid physical construct but it's what everyone claims. Do you expect someone to twirl their mustache, furl their cape, guffaw in laughter and snark on how much of an evildoer they are?
Everyone wants to think they were in the right. It's almost as if the theoretical is immaterial.
Let's take the horrible crime of rape for example. Some teenagers are quite a bit larger than adults and we can theoretically imagine a child offending an adult but we've decided that's so unusual that we defined a presumed relationship (of the child being the victim).
This is completely reasonable because the conceit of agreeing with the mental exercise doesn't dissuade us from the historical and practiced reality of sexual crime against children being so dominant that it's presumed unless extraordinary evidence is presented otherwise. I'm sure a quick Google search will reveal these unusual exceptions because it's a "man bites dog" kind of story for journalists. The fact they can be itemized as individual stories instead of presented as a statistic is evidence of its rarity.
Self defense might be similar. Perhaps the relationship is mostly aggression and antagonism. There's an occasional zebra of a true self defense where someone jumps out of the inky shadows to subdue an innocent damsel but perhaps we need to set the bar in the court of public opinion far higher (in the legal court I believe it's already quite a gambit but IANAL)
