This could be an interesting way to measure mindkilling. Get people from different groups, let them hear white noise or see random points and ask them to report how often they hear/see messages offensive to their groups. (For example how often a fundamentalist religious person would hear/see indecent or satanic messages.)

Indeed. When we are talking about facts about reality, then these kind of things become a problem. When we are talking about people's critical response to the text, then if someone has that response to a text, then its there for them at least. If multiple people do, then we can argue that

a-there's something about the text which causes this reaction in a subgroup of people b-this subgroup of people would have this reaction to every single text.

I assign b a lower probability because this is a reaction borne of particular chapters rather than the entire novel.

Are we talking about whether or not a measurable phenomenon exists, though? I thought we were talking about a completely subjective kind of thing. You can control for whether or not people are judging levels of sound or patterns or physical comfort inaccurately due to some bias, but is there even such a thing as judging their own emotional reactions inaccurately due to some bias?

I get something like that on an airplane or bus every once in a while. I usually spend about a minute trying to exert some control over the process, but I've yet to internally locate the on/off switch for that version of it. (it's not a normal ear-wig, which can be defused by forcibly thinking of a different arbitrary song; it's confined to what may or may not be the harmonics of the vehicle I'm on.)