I'd be interested in a robust defense of the claim that refusing to have a trigger warning, in the context of this post, is not deceptive. The arguments I see

I'd be interested in a robust defense of the claim that refusing to have a trigger warning, in the context of this post, is not deceptive. The arguments I see for not having one are: too few people would care so it's not worth inconveniencing the many for the few; there's already informed consent and so it's useless; and the talk is not harmful to anyone. (I think I had another minor one in mind but can't recall right now.) 1 is possible, but is not the one made by OP. I've argued against the premise of 2 (which the OP did make); if you have a more deontological worldview, you might want to frame this as the student's "own fault" for not realizing, but I generally don't blame people for being dumb (in the sense of insisting on them bearing the consequences of being dumb), instead asking which course of action yields the best consequences. In this case, if we assume informed freedom of association is a value, then adding information is a benefit. 3 would be a good defense if done well, but again, isn't the OP. It would actually be the best example of "I'm not a jerk"-type answers. But it's not immediately obvious how we can view something that bothered someone as not harming them. At best, you'd probably need to invoke Christian beliefs and go back to "informed consent" as above. Presumably you concede that Christians shouldn't do this to outsiders, and so the issue is about what counts as informed consent.