Earlier quoted context omitted.
It doesn't surprise me that people with larger overall vocabularies also have larger swear vocabularies. But the study you cite deals only with taboo word fluency, not with actual usage. I would be curious whether high-vocab swearers diverge from low-vocab swearers in how they actually use bad language. In my experience, even my high-vocab friends drop f-bombs in substantially the same way that lower-vocab friends do…
I hypothesize that the "swearing => stunted vocabulary" argument is just a post hoc rationalization to give some justification for not liking bad words.
There are two distinct populations (in UK), those of poor vocabulary who use swearing all the time and don't seem capable of speaking in a nuanced way. And those who have the vocabulary to not swear, can still express themselves without expletives but choose to use them depending on the company/context they're in.
I found as a teenager that I'd swear to try and appear cool, and when I lacked sufficient nuance to my vocabulary to clearly express my feelings, and decided I wanted to do better.
I don't really care if you swear - except in front of children (because they have to learn not to swear in the wrong context when they can get in trouble from others who are more conservative) - but unless you demonstrate otherwise I'll assume it's lack of decent vocabulary.
Almost all people I've worked with who've sworn a lot (amongst general company) have had very low levels of education.
I don't really understand the whole "these words are shocking" attitude, eg cunt, people give simple utterances too much power.