The non-aggression principle (NAP) states that the only legitimate violence is self-defence. This includes both physical and psychological aggression.
In the past the principle of freedom of speech did protect all speech, including offensive speech. Nowadays we see this principle being more and more softened to the point where only pc speech is thought to be legitimate speech. We still have the rights to offend anyone we like, but this might end in a couple of years.
What does the NAP say about political correctness and trigger culture. Is saying something that is offensive to some groups violating the NAP and should be considered to be immoral? I would argue otherwise.
The NAP protects the most fundamental rights of humans, the exclusive ownership over our bodies and the ownership of our work. Violence is opposed to these rights since it is used to dominate and control others. And for this it does not matter if the violence is physical or psychological. But most bad speech is not used to control others and does not fall under the NAP.
Let me give two examples.
- I am in the pub with my friends and tell a sexist joke. We all laugh and at the next table there are some women that are offended. In this situation there was no violence. I have a right to offend others and others have a right to be offended. It may mean that I am an asshole, but I am not violating the NAP
- I am the boss in a company and psychologically mistreating an employee. Here I try to establish dominance over the person and psychological aggression is not really different from using physical violence or threats. This case violates the NAP.
In summary, in my opinion the NAP also applies to psychological violence. But that does not mean that we have a duty to conform to pc culture. We have a right to be offensive, we have a right to be an asshole, other people have a right to feel offended. Psychological violence is not a collection of stupid jokes, it is when people try to mentally destroy others with the plan to establish dominance and control.