LOL, that's cute. Never could understand why a word which can be aptly used to describe an action absolutely essential to all of us banging here - ooops, make that - being here could be seen to be a dirty word. This .. https://slate.com/news-and-politics/2007/06/how-does-a-dirty-word-get-that-way.html .. really doesn't help much except to tie it too another nonsensical nonsense, that we are all born sinners.
So one suggestion is that fuck was born as a bad word, as we were all born as sinners. Always felt it had something to do with religion.