I do not like this line of reasoning because it basically advocates walking on eggshells around everyone since it is not possible to model the potential fragility of mind of billions of humans.

I read some arguments that being drive-by downvoted without comments somehow made people unwelcomed. And you add to that that this is practically a form of PTSD.

If I am supposed to model people at the other end of the screen as "my downvote might trigger PTSD" then, mildly put, I do not find that model to be very helpful. I can't quite put my finger on it, but it seems like some sort of game-theoretic trap.

Disclaimer: I don't see myself as a kind person and asking me to spend extra mental energy just to be nice is like asking for a pound of my flesh. Thus the above may be motivated reasoning to ignore people who complain about the lack of kindness.