From what I can tell, most adults don't have a problem with swearing among each other, but for some reason it's scandalous to swear in front of a child. This idea is not only baseless and absurd but harmful.
Words are arbitrary sequences of syllables agreed to represent something. The word "fuck" for example expresses anger or other negative emotions, which are, of course, a ubiquitous part of life and not "bad" at all. Saying "fuck" does not make a person angry or violent any more than searching for a job makes someone unemployed. "Fuck" is an expression of perfectly normal human feelings, and no, it's not an unnecessary expression; you really can't achieve the same thing at all with different words. Saying "I'm very angry" sounds particularly not angry.
What happens when you discourage yourself and others from using these words when you would like to? The same thing that happens any time you bottle up a negative emotion: it gets stronger and eventually will be expressed in some form or other. Training oneself and others not to express emotions is harmful and evil. Training only some people to feel disallowed from expressing their emotions is even worse, because they'll see the unfairness and it won't be them who's to blame when they grow more and more disconnected from their parents as a result. Although, if their parents are the kind of people who believe that it is somehow unacceptable for one person to use a word in a given situation but acceptable for others to use the same word in the same situation, that's probably a good thing...
There is such a thing as a "bad" word. Here are a few examples:
Words that represent a concept that isn't real, like "redeem" which because it's grammatically transitive allows the incoherent idea that you can be redeemed by someone else's actions
Words that represent a concept already represented by another word giving the impression that there's a difference where there isn't ("taxation" and "communism")
Words that represent multiple different concepts and muddy our thinking, like "good" which refers to both morality and happiness - wonder why so many people are utilitarians?
Swear words don't fall into any of those categories. They are in fact very good words because they do in 1-2 syllables what is difficult or impossible without them.
Now this doesn't mean we should use profanity in every sentence like some people do. The usefulness of profanity is to convey things stronger than can be done with normal words, and so if you use them too often, they start to lose their impact. It's wiser to use profanity sparingly so that we have access to extreme language when we need it.