Though I mentioned humour and fitting in, you're right that I didn’t really address the use of profanity to build rapport/break down formality/establish intimacy, and adjust the tone of a conversation in other ways. (Some aspects of that were on my list of things to add, but I never got around to it.)
> I get the feeling this guy doesn’t have too many close friends.
Thankfully, despite this essay & other indications to the contrary, I have a reasonable number of wonderful close friends (I’m sometimes as surprised as you), some of whom swear, and some of whom don't. I sometimes appreciate swearing, and sometimes find it grating. But I find that overuse of swearing usually detracts from a conversation, which is why I wrote up my argument for why there are potentially maybe possibly valid philosophical and pragmatic reasons for adults to consider swearing less.