Er…
That aside, how much should someone be beaten if they follow someone? Is there a point at which they can fight back?

I am not making a legal argument. My point is, if some women you car about is in a similar situation, do you tell her to not act unless the person assaults her first?
Yes, absolutely.

And many people would. The question is not what is legally permissible, but rather what is foreseeable.
The term for the people who’d punch him in the face is “criminals”.

But how do you know he isn’t gonna run right past you? What if he stops short and asks you for help because some guy robbed him? Again, this is where you are trusting your judgment on what someone else’s motives are is accurate. You assume someone running towards you is an imminent threat, yet you deny Martin that same latitude regarding a guy following him at night for apparently no reason.
I can’t even visualize what you’re trying to describe here…someone is running at me, and I run back at them and punch as we come together? A punch is good for about three feet; if someone is running at you and gets within three feet, their stopping short is no longer an option for them. That’s going to be an impact.

No, but for many people, it heightens the situation. Do you think a heated verbal argument between an unarmed person and one with a gun proceeds in the same fashion and tone as one between 2 unarmed people?
The key to keeping heated verbal arguments from turning violent is for none of the participants to escalate the argument into violence.
This is why I find your musings here so wrongheaded: you are advising people to start a fight if they think someone might, at some future point, attempt to harm them, as opposed to as someone is attempting to harm them. That is horrible, horrible advice: it turns misunderstandings (turns out that guy’s not following me, we were going to the same store! That guy’s my new neighbor, that’s why we both went to the front door of the apartment building! That’s just a jogger, he’s not running at me!) into violent showdowns, where people get hurt or killed. People have a profound ability to be oblivious to their own actions and how they might appear to others. The only sane and legal advice is to never escalate something into violence unless you face an immediate threat.

Geez. I am not interested in what you can get away with in a court of law. I am asking you if you think it’s right. the legal questions have been settled for the most part. The question is why you think the situation occurred as it did, and where there is fault.
It’s wrong and illegal to use force on people that aren’t an immediate threat to you.

Cite?
Use the reasonable person test.