Damn vs. Dam

So, I'm not much for swearing, and I definitely do not swear in front of my children. But this morning Daniel was driving me CRAZY and Abby was not helping matters. He wanted a shark book and Abby didn't seem to want him to have it. I ignored them for awhile, but then couldn't take it any longer. I slipped and said, "Abby, give him the damn book!"

Daniel immediately said, "Yeah, give me the damn book!"

Abby and I burst out laughing. I explained to both Abby and Daniel that I'd used a bad word and that they should not use that word. Abby being Abby, she immediately launched into an explanation of why "dam" is not a bad word and that she uses it all the time and should be allowed to continue to use it. I agreed that when referencing a structure built to hold water back, it was fine to say it.

She then wanted to know why it was a bad word, and I was stumped. I could not come up with a plausible explanation of why damn is a bad word.

Any help would be appreciated.