When did the term mutt start to be so terrible? and more importantly, why????

isnt a dog a dog? doesnt every dog have the same heart, the same brain capability, the same love and care? why does it matter whether your dog has pure blood or mixed blood? isnt that almost discrimination? not appreciating something because its ethnic backgrounds arent entire? why does a dog have to be a purebreed to be important? so many dogs are mixes that have helped america SO MUCH and yet still, people think that if your dog isnt this fancy schmancy pup with these bloodlines you can trace back to before Queen Victoia its just dirt to them? its like saying, "oh, Lola, i cant trace your family back to caveman times, so i guess that means that you are less than me, even if you may be nicer, smarter, and healthier and maybe even more beneficial to the world than me" im not saying purebreds are any less than mutts, but i think that all dogs are equal! heck, my friend has a purebred Pitbull and its the nastiest rudest dog ive ever met! and my other friend has a mutt and its so sweet!