Your examples are cogent, and I understand them.
What I don’t understand is situations that don’t exactly have an “initiator”.
Example: when I lived in Brooklyn, I used to cross the street a lot. If an armed citizen does not cross the street, and the inevitable bumping and name-calling starts, when is the threat enough to use deadly force, and does SYG imply that you were right (by the law) to walk into a situation that you knew, or should have known, would escalate?
“No duty to retreat” sounds clear, but lots of street hassles start with failure to exercise common sense and good judgement. That’s not “aggression”, but it could sometimes be “initiating”.
I understand about SYG in your home not being absolute, I was generalizing. If you kill your daughter’s boyfriend, I imagine the DA will have a few questions. If you kill three armed Amish at zero dark thirty, not so much.
The threshold legal label is "aggressor," and represents a line that amounts to undertaking or threatening unwelcome contact. Sometimes the action that represents "aggression" is left to the jury, but generally it is some sort of unwelcome contact, outside of social norms.
Trying to plant an unwelcome kiss can be shoved off - the person doing the shoving is justified, as a method of warding off unwelcome contact. But, if you are in a crowded space (store, disco [heh], airport, sidewalk) and are jostled, you probably don't have the right to use force against the person who bumped you, or touched you to let you know they were there, etc.
Name calling is not aggression, under the law. Only the threat or use of force, contact, etc. So, that "bumping" comes to mind as a possible unwelcome contact, entitling you to use force to prevent the next bump, or even the first one.
You raise an interesting quandary, discretion over being in the legal right. Being disposed to initiate use of force or even violence is used as a tool of intimidation, and the groups you describe do so with legal impunity. The law more or less allows that sort of thuggish conduct in fact.
But approaching that group, even against prudent judgment, is not initiating the use of force. You have a right to be there, and if they initiate force, you are allowed to use force to ward off their unwelcome advance. You don't have a tit-for-tat right, nor a right to use force as revenge.
Serino tries to make the legal test into "could have avoided the outcome." That legal test has all manner of pitfall, and looks a bit like your question about "initiating" action that leads to a bad outcome. The law draws a bright line that roughly resembles a right to go about your business, and grants a legal privilege to use force to ward off contact that would be illegal (assault or battery). The threshold to allow deadly force is (reasonable - meaning the jury decides) belief that such force is necessary to avoid serious injury or death.