Oh Mother

How is it that "mother" became an insult, as in "a real mother of..." or "you're a real bunch of mothers"? I know what word mother is short for here and I have no intention of rehearsing how it came to be shortened in common parlance.  But, once the word had been shortened do those uttering it as an insult not notice a strong similarity of the word "mother" to the word "mother"?
Recently I was stunned to realise that the phrase "your mom..." or "yo' momma..." if said with a certain inflection is also an insult.  Apart from anything else, it's only a phrase, not even a complete sentence.  Apparently it calls to mind such gems, and I mean "gems" in the sarcastic sense, as "your mum is so ugly, when she was born the doctor slapped her mother."  But the sentence is unfinished often, how then is it an insult?  It is an insult because it is understood by both parties to be an implication of a perjorative and defamatory statement about said mother.  How have we come to this?  Can't we just love our mothers and have respect for each others'?  Please.