No, it isn't harmless. It makes many cringe because of the love they have for God. It'd be like someone calling your gramma vulgar names. Yes they are just words, but they would invoke emotions inside you because of the love you have for your gramma.<quoted text>Are you saying that when I say "god dammit" I am hurting you like I might hurt a child by saying "I hate you"?
Surely you have heard the phrase a few times. And since I am an atheist it really is a meaningless thing for me to say anyway.
I assure you it is harmless.
I personally feel it is the worst thing that could be said in the English language. Be aware, what you feel is harmless, is offensive to others.