because of the quality of your dogs. They want to try and give you a bad name or something because your dogs are better than theirs and they feel threatened/jealous. Sort of a "conspiracy theory" but really the only thing I can think of as to why someone would say something about YOU of all people. If I want to give someone an example of a responsible breeder, YOU are who I think of.
Do you have older pups that just wouldn't sell, waiting to be sold? NO!
Do you give your pups to just anyone, because you have a hard time finding homes? OBVIOUSLY NOT, as you have a long waiting list.
I say, if YOU feel it is the right time for a litter (which it seems like you do), GO FOR IT and to hell with what any of the naysayers say!