Ok, so your definition of a responsible breeder is different than mine. In my book, a someone who is responsible doesn't kill someone because they are ugly or don't look right.

Take my breeder for instance -- she doesn't intend to breed homozygous merles, but in a merleXmerle breeding, sometimes they pop up. Does she kill them? Nope, she finds a good home for them. And I like her for that.

I have to admit I don't know much about cancer. Is it a genetic disease?
Yes it is. I believe that my Leather actually got it because she wasn't spayed until she was 7. My dad was going to breed her. But he says he doesn't remember what kind of cancer it was, so I can't say for sure. But cancer and tumors are genetic.