I don't disagree with you but that study seems like fucking bullshit.
Using the tactic you disagree with to drive your point home. Well played.
A calm well spoken person grabs a lot of positive attention with an F-bomb carefully dropped. The step out of character alerts people that something must be serious.
...
That report doesn't say what you want it to.
"Honesty" is not necessarily reality. Someone who is moved to high expressiveness is plausibly sincere, but they are not necessarily rational, reasonable, or correct.
Appealing to emotion works but it is still a cheap trick. If that's what we do here nowadays, well OK, but it's a loss.
No, that's a puritan misconception.
Not only is a powerful (and culturally significant) method (as opposed to some mere trick), it also has evolutionary and psysiological benefits.
Among tons of other things:
https://en.wikipedia.org/wiki/Hypoalgesic_effect_of_swearing
You're thinking of blasphemy. "Vulgar" means "coarse" or "unrefined". It used to mean "concerning the common language", i.e. as spoken by ordinary people; not the literary language, or the legal language, or the clerical language.
Actually vulgarity was invented (and has historically been used) to improve the weight of such messages. It works too:
"Writing in the journal Social Psychological and Personality Science a team of researchers from the Netherlands, the UK, the USA and Hong Kong report that people who use profanity are less likely to be associated with lying and deception." [1]
Can't argue with fucking science.
[1] https://phys.org/news/2017-01-links-honesty.html