And the answer to your question, when you get down to it, is respect. If you don't think respect is needed in today's world than I have no other answer for you and there wouldn't be anything else for me to add on the subject.
Okay, we need to clear this up.
First thing I want to say is that I DO think respect is important in a modern-day society, and I would never argue otherwise.
What I would contest however, is that NOT EVERY IDEA OR BELIEF DESERVES RESPECT.
Should we respect the belief that white people are better than black people?
Should we respect the belief that men are better than women?
Should we respect that belief that The Theory of Evolution is a hoax perpetrated by the Scientific Community to destroy Christianity?
Clearly, not all ideas are deserving of respect. I will agree with you on one aspect: That we shouldn't be going out of our way to offend people either.
But these are two different issues: Not having respect for somebody's beliefs and going out of your way to offend them.
I don't have respect for the belief that there is an invisible man who lives in a fiery place and punishes bad people (Satan). I think that's childish and ridiculous and there's absolutely no evidence for it. I don't think naming fictional items after said fictional character is disrespectful either. Naming fictional items after fictional character is (in my understanding) not a blatant attempt to attack a certain group of people's beliefs. Now, if for example you were to name an item "Satan-Worshipper", then you're traveling into territory which is just becoming outright offensive on purpose.
That's just my opinion on the subject. I don't think using the word "Satan" in a video game is attacking the beliefs of a group of people any more than drawing a simple picture of Muhammad. Can you take it to the next extreme and start trying to offend these people on purpose? Yes, and then I would agree that you're being an ass.
Is swearing by some characters realistic some of the time? Sure, but as the content creator you also don't have to.
Well you don't have to, but then you're removing an aspect of personality and realism from your game just to please a small group of people's sensibilities. Have you ever read "Of Mice and Men" by John Steinbeck? This is a classic piece of (fictional) American Literature where LITERALLY every other word from the two main characters is a curse word. I mean it is so fragrantly over-the-top in its use of cusswords that it could probably offend a mob-boss. But why does the author include this harsh and offensive language? Because he was trying to make the characters as realistic as possible for the setting he had created. People cussed at that time. People STILL cuss. I would venture to say that MOST people cuss (at least in America). To make a piece of work that didn't include that aspect of the culture would be to make a piece of work that alienated the audience in a way, by making the characters they are connecting to unrealistic.
Is it unprofessional? I could see arguments for both sides. It's certainly not unprofessional to include cussing in a movie to make the characters more realistic.
I agree with you that there should be an option to turn it off.