This is a really good question. It's sometimes hard to trace the roots of terminology or movements to a singular event/time pre-internet. It's interesting because ideas like "micro-aggressions" did not exist until circa 2012 and this is verified via Google. But political correctness pre-dates the internet.
Growing up in the 90s everyone was taught "sticks and stones will break my bones but words will never hurt me"... kids are taught the literal opposite today. They're told their verbal actions can be considered "violence" that does "irreparable harm" to someone.
The 'old left' view held famously by Hugo Black among others was that the whole point of free speech is to protect the person who thinks differently. This includes
cultural pressure as well as legal injunction, as Tocqueville and Mill understood.
Many 'new left' Marxists, particularly in the academy, rejected all of this in the 1960s. Herbert Marcuse introduced the idea of "repressive tolerance" which is basically a Marxist rejection of free speech as serving the interests of the bourgeois and status-quo forces in a society. 'PC culture' is a crude application of this sort of theory (e.g., white men are not allowed to hold opinions about topics such as affirmative action).
It is very difficult to have an adult discussion with students about serious topics when they are so delicate and cannot handle hearing an opinion other than their own expressed. As I said earlier in my experience ND students are much better at handling disagreement than students at other schools. The reason for this in my view is that a lot of the students here are conservative and so there are decent odds you aren't the only person arguing from that perspective. At typical schools the would-be conservative or libertarian students who reject the diversity cult are so few that the
Asch effect kicks in and they are afraid to express a different view.
Why does this bizarre behavior on campus matter? One reason is that our entire political and legal system is based upon argument and
division. Can today's college students sustain that culture and its institutions? Don't count on it.
And by the way, when they do start passing 'hate speech' laws, which are commonly used in other countries to repress unpopular opinions, the First Amendment will not save us. These people
will be (in some cases already
are) the judges who will be enforcing these provisions.