The way this is typically framed is "impact matters more than intent". Like if you weren't watching where you were walking and accidentally stepped on someone's foot. You didn't _intend_ to harm them, but the overall _impact_ was that you did harm them.
As you rightly point out though, the elephant in the room is that impact in this context is not falsifiable. Unlike stepping on someone's foot where you could use instruments to measure how many capillaries were broken or if the bone is cracked, with words and feelings you can't actually empirically prove harm was done which is why I think enacting laws and policies that directly correlate with impact is a recipe for disaster...
IMO the best way to deal with impact has to be at the cultural level. "Hey, I find swear words offensive, can you stop?" "Oh sure, sorry about that, I won't swear around you". Bam, problem solved.
A society that transitions to: "Hey, I find swear words offensive, I'm going to report you to the psychological harm police" is one on the fast track to dystopia.