Emphasizing moral taboos like "cussing" can lead to bad moral priorities.
Jesus described some things as gnats and some things as camels (Matt 23:23). He chided the Pharisees for the amount of effort they put into avoiding swallowing "gnats," but how they exerted very little effort at avoiding swallowing "camels." Doesn't some people's attitudes and behaviors about cussing fall under this same scrutiny?
People walk out of movie theaters when there's cussing, but how do those same people feel about millions of children dying of preventable diseases? People would likely be shocked, offended, and even walk out of a church if their preacher were to cuss from the pulpit. Would they react at least as offended if he were to say in a subtle way that they had little or no obligation to help the poor?
People can become so offended by hearing cussing that they will confront complete strangers and tell them to stop cussing. Do they become at least as offended when people are unforgiving or unmerciful or indifferent toward each other? People get alarmed when they can hear their neighbors cuss outside their houses. Are they equally as alarmed that their neighbors are not followers of Christ and may be eternally lost?
Is some arbitrary word-list that we deem offensive really as important as the rest of these things? If it's at least equally important, then why don't our reactions to all these things reflect being equally offended? i think it's arguably the case that these other things are more important than cussing, yet it's certainly not the case that people on the whole act more offended by those things than by cussing.
We would get up and stomp out of a church in a huff if a preacher cuss, but we're perfectly content to sit in a cuss-free church service all the while bearing a grudge against someone in the room. What does that say about our moral priorities? What does that say about what matters most to us?