People make harmless jokes that are applicable to your life at a daily basis, you're just not party to them. Thinking a joke is dangerous just because you observe it is a base rate fallacy.
But, at the same time, thinking that "a joke" is safe when observed, is also not necessarily true.
Good judgement needs to be taken into account. I recall having to "reapply" for my temporary job in the computing center every semester (because, of course, it was "temporary") - and one of my fellow students, after having done this for a couple years, and having a bit of ego, basically just scrawled on his application form, "Hire me again or I will murder all of you." You see, if you knew him, it was actually really, really funny. We were all a close group, and everyone on the team thought it was hilarious. The HR organization that unbeknownst to this student, screened all applications, and had no idea who he was, took a decidedly different perspective on his application.
The proper response was to alert security, and thankfully his hiring managers - who then de-escalated the situation.
The problem with the airline situation - their is no easy "oracle" who can confirm that this person is most decidedly not a threat.
People in general are very afraid of flying despite the fact it is reasonably safe. Making a joke about fucking with an airplane is in poor taste considering many people are on edge.
It'd be like making a rape joke when you pass a woman on a dark street.
It's just a bad joke. People also have an obligation to control their own hearts instead of waiting for someone else to tell them how they should feel.
It's not my job to make anyone feel safe. That is merely the bias of my personal style. Pure coincidence. The fact is, talking about religion with derision could incite violence, pain, and fear. Am I someone who gets off on pain? No. But I'm not going to go out of my way to protect someone's heart either. It's their job to rule their own heart. It's not their psychiatrist's job or their pastor's job. On a side note, I would add that many religions go out to deliberately propagate fear ("Jesus is the sacrifice to save us from hell"). Nobody cares. I have a friend who is really pained by the thought that he can't convert his close friends, and worse of all, his parents! What agony he must go through now that somebody decided to exercise their free speech and tell him about the eternal torture of hell. It was his job to rule his own heart.
Similarly, it is not the job of students to avoid discussion of rape on campus because the mere mention of rape could cause a reliving of trauma. It is instead out of personal will for a healthier future that we deliberately choose superior speech over unrefined speech.
It is okay for society to shame those they think are tactless. It's not okay to bring logistical or material pain to someone's life because they made one feel terror, or angst, or outrage. Discussion of hell could bring more pain into someone's life than most other subjects one can summon up without a priori knowledge.
