If I don't understand what a Frenchman says to me, that means that I don't understand French, not that the Frenchman isn't being clear and effective.
One guy responded by saying,
Speaking French or a strong dialect isn't analogous to swearing in English. It's the use to which the language is put, not the language itself that counts here. Some confusion can arise when using swear words (and, indeed to many other imprecise iterations) because they often are used as 'blanket' words. 'Fuck you' is a imprecise blast, used with strong feeling to express distaste of a particular action. It would be more accurate to specify what caused that reaction. The precise response may be not as satisfying or be able to put across the strength of feeling, though.
Yet another person said,
That's a false analogy and you know it. We're not talking about situations wherein people are using unfamiliar words or grammar. Rather, we're talking about situations wherein words are used indiscriminately, thereby robbing them of their impact and the ability to accurately communicate shades of meaning and emotion.
The problem lies in the indiscriminate use of this language. If you routinely use the word "sh*t" to mean excrement, something detestable, and just plain stuff, then the word loses its impact. Far from enhancing accurate communication, it simply serves as a barrier.
This problem isn't merely limited to profanity, BTW. The problem exists even within polite language. For example, I knew a graduate student who routinely described software designs as "good." His use of the word may have been accurate, but it was imprecise. A more effective communicator would be more specific, describing the designs as elegant, or efficient, or perhaps highly maintainable. The descriptor "good" lacked those nuances of meaning, and its indiscriminate use only aggravated that problem.
That's why it's a cop-oput to say that profanity is an excellent means of communication. It's only advantageous if used sparingly. When used indiscriminately, it blurs the distinction between truly aggravating circumstances and minor annoyances -- or worse, the humdrum routines of life.