Looks like you've done some serious research (or picked it up in Nuts) whereas I had not really given it that much thought, nor heard Shane McGowan's comments.
Isn't it just a word that rhymes with maggot
Isn't it a song centred around a couple that for years had their ups and downs, slinging insults at each other in a drunken rage.
This this is a song, a performance not too dissimilar to what goes on in Eastenders or Corrie. Gratuitous violence is commonplace on telly, shouldn't it be treated it the same?
As for Shane and the interview where he says what you say he says, I'm guessing it was the first thing that entered his pickled brain, especially as the interviewer (daily mail?) was buying.
He said the right thing.
Far worse stuff played / shown by the BBC over the years.
Attention seeking, non story, moral high ground, sells papers, takes heat off what really matters in this day and age... take your pick.