In not familiar with exactly what happened that night but just an uneducated guess:
All of the threats that Kyle encountered was in response to the fact that he was playing Timmy Toughguy and actively strolling around with a gun…
If he was just wandering around being an unarmed cunt then the chance of being swung at is still not zero but pretty damn close to it.
If at any point he ran - and kept running, or dropped the gun and ran, fully retreating from the crowd I doubt he would have been chased too far and the need to shoot would have been eliminated
In the same way he (correctly) saw others as a threat, the primary reason he was being threatened was because everyone else saw a random civilian with an assault rifle that was a 50x larger threat well before they threatened him. Even if he intended to do nothing with it, he knew he was sending a threatening message just being there with it and he then seemed shocked when people started responding to that threat - of course they would try and disarm him at a bare minimum.
The threat to Kyle at this point was genuinely high because most adults in the US - or anywhere - instantly recognise what a random civilian in public with an assault rifle means - mass shooting. This is exactly the message Kyle intended to send in order to scare rioters off. If he wasn’t there just to scare people off then he was there to actively murder people. At this point I could put it down to a dumb kid making a really stupid mistake. Maybe worth a few years in jail for gun charges or inciting violence?
But he didn’t retreat as he was being threatened - a fraction of what he was threatening others. He chose to attack instead and it’s at this point he deserves to spend the rest of his days rotting in jail. He tried to send a message, that message wasn’t received so he murdered those who were fearing for, and attempting to protect their own lives.
Kyle choose to be the aggressor - and much greater threat to anyone there - from the start. He wasn’t protecting his own family, house or neighbourhood, he crossed state lines to be an aggressor. Kyle continued to act as the aggressor at every stage of the encounter.