Who has argued otherwise?
It’s not. Many people at some point just developed a habit of using curse words. I may turn to the guy beside me and say “its fucking cold in here” totally without thinking, not trying to be cool or to be offensive, just that type of usage is second nature. Millions of people think nothing of it, millions don’t like it, true.
I agree that you should respect society’s rules, even if you don’t agree. If I was sitting next to a nun, yes I might try and think before I speak, so as not to offend someone, but also I don’t feel if I slip up and say a curse around her that she should be bothered by hearing me say something not directed at her in any way.
I don’t think there are very many, if any, adults who curse a lot who do it to purposefully offend. If saying fuck at my job was a firing offense, at some point I would drop something on my foot and get fired, just because its second nature to me to say a curse in that situation.
And if you sat near me and told me the word pencil offends you, I would think it odd, sure, but would try to not use it around you. But I wouldn’t expect your world to end if I slipped and said it 
WeeBairn, that is a very reasonable attitude and a very reasonable explanation. Junior high kids start to swear because they think it makes them sound cool and grownup and tough, and for some, it turns into a habit they never break. Those aren’t the ones I don’t understand. I don’t get the ones that can thoughtfully remove one word from their vocabulary because it offends someone, but they get so emotionally attached to another that they simply refuse to restrain their use of it, even knowing it’s going to offend people.
Marley23, nobody has argued otherwise. Many have argued that those millions shouldn’t be offended or insulted, but I haven’t noticed anyone arguing that they aren’t*. That, however, wasn’t the point. It was the background information preparing for the point.
I also subscribe to theory “someone (or something) can’t bother you unless you allow it”
The content of broadcast media is special because the electromagnetic spectrum is a shared resource that goes right through your body whether or not you want it to. Take the extreme example of the shortwave radio frequencies, at which signals travel around the entire world. There is only one 10 MHz frequency, for example. So it’s like “the oceans” or “the (world) highway system”. Society finds it practically necessary to regulate for the mutual benefit of all. What is allowed on the broadcast spectrum is vetted in some sense, and groups with some legitimate claim to taking offense have a legitimate complaint that deserves consideration, and depending on circumstances may deserve policy change.
This is different from, for example, a web site or a cable TV station. These things, you have to connect to. These things, you can take or leave.