People jokes about dead. People jokes about sex. People jokes about anything. On the contrast, if some group of vulnerable people are in some protected zone that cannot be joke around, then it is in fact the society does not accept those people are the same as other people. It is a kind of positive discrimination. I mean, putting anything too far is bad.

And do the speaker insult people with PTSD? If no, then why being triggered, specifically if you don't have PTSD?

Did you just imply that veterans of the UNIX wars can't have real PTSD?

I think jokes should be told on the appropriate place, and maybe conferences aren't the place for them.

However I am fully against political correctness and censorship of jokes.

I don't miss what my parents generation had to endure.

Here, watch this and lighten up a bit: https://www.youtube.com/watch?v=G9n8Xp8DWf8&t=2m13s

He say "post traumatic stress", not PTSD. It's possible to have psychologically issues from seemingly innocuous experiences.

Or maybe they're thinking your fixation on an unrelated detail is harming the potential on-topic discussion for them.