Whats the big deal about BYB'S?

I always see everyone freaking out on others about bein a BYB and having mutt puppies. I bet more then half the people on here that give others crap about being a BYB have a "mutt". Mutts and puppies from the BYB's are some peoples best friends. I am just curious whats the big deal about letting your dog get pregnant and have the puppies as long as they go to a resposable home.