I would suggest that another trend which contributes to this "one bad fight" is the growing personal disposable income in the US, which allows parents to be highly litigious, demanding things like arrests of kids their kids get in fights with:
Anecdotally, teachers have been talking about fear of getting sued by parents for a long time now. I suspect this is a big driving force behind the "everyone gets a trophy" mentality and not at all liberalism. Teachers have been kowtowing to moneyed tiger/helicopter parents in ever more egregious ways.
https://fred.stlouisfed.org/series/DSPIC96
Anecdotally, teachers have been talking about fear of getting sued by parents for a long time now. I suspect this is a big driving force behind the "everyone gets a trophy" mentality and not at all liberalism. Teachers have been kowtowing to moneyed tiger/helicopter parents in ever more egregious ways.
My own pet theory anyways.