OP started by describing how that wartime friend/enemy mindset more accurately describes the extreme lefty behaviour we've seen lately than any kind of disagreement between countrymen. It's not technically a watertight thesis yet, but it's not unreasonable.
And then OP tried to use their wartime experience to explain how that level of commitment to force trumps everything but an equal commitment to force. Violence is the fundamental unit of human negotiation, because once you're physically incapacitated you have no say in what comes next, everything else above that is just obfuscation of that fact by mutual agreement, typically for overall net benefit to all parties.
Once that mutual agreement is broken by one party seeking material gain, then the other party needs to be willing and able to return violence in equal or greater measure so that sitting back down at the negotiating table becomes the materially rational choice. And the more you let them hurt you before you find the will to retaliate, the less able you are of actually forcing them to stop. There will always be people with no natural inclination towards peaceful coexistence unless it materially benefits them, those who most desire a peaceful existence must understand the necessity of demonstrating a communal ability to enact such effective violence that peace becomes a matter of self-interest even for those for whom it's not a matter of principle.
Now really the reluctance to commit violence is more of a spectrum than a binary, so even for the more violence inclined the will needed for the first punch is way more than the next hundred. So if they've already thrown the first punch you'd be a fool trying to negotiate them out of punching you again without providing some form of physical deterrent, and since any single punch can end you, you'd also be a fool to stop and offer them a return punch every time, you rain down retribution without reprieve until they surrender or are incapacitated. On a group level, if anyone cheers one of their own group throwing the first punch at you, then they've also already crossed that emotional Rubicon, so you can likewise consider them unable to be stopped by anything but an equal or greater threat of violence towards their group, waiting for each of them to strike first is begging to be crippled before you can fight back.
OP started by describing how that wartime friend/enemy mindset more accurately describes the extreme lefty behaviour we've seen lately than any kind of disagreement between countrymen. It's not technically a watertight thesis yet, but it's not unreasonable.
And then OP tried to use their wartime experience to explain how that level of commitment to force trumps everything but an equal commitment to force. Violence is the fundamental unit of human negotiation, because once you're physically incapacitated you have no say in what comes next, everything else above that is just obfuscation of that fact by mutual agreement, typically for overall net benefit to all parties.
Once that mutual agreement is broken by one party seeking material gain, then the other party needs to be willing and able to return violence in equal or greater measure so that sitting back down at the negotiating table becomes the materially rational choice. And the more you let them hurt you before you find the will to retaliate, the less able you are of actually forcing them to stop. There will always be people with no natural inclination towards peaceful coexistence unless it materially benefits them, those who most desire a peaceful existence must understand the necessity of demonstrating a communal ability to enact such effective violence that peace becomes a matter of self-interest even for those for whom it's not a matter of principle.
Now really the reluctance to commit violence is more of a spectrum than a binary, so even for the more violence inclined the will needed for the first punch is way more than the next hundred. So if they've already thrown the first punch you'd be a fool trying to negotiate them out of punching you again without providing some form of physical deterrent, and since any single punch can end you, you'd also be a fool to stop and offer them a return punch every time, you rain down retribution without reprieve until they surrender or are incapacitated. On a group level, if anyone cheers one of their own group throwing the first punch at you, then they've also already crossed that emotional Rubicon, so you can likewise consider them unable to be stopped by anything but an equal or greater threat of violence towards their group, waiting for each of them to strike first is begging to be crippled before you can fight back.