This is one thing I really don't get... although I'm not very well read up on the subject, so maybe I can't comment.

...I'm a moggie lover, always have been, always will be, but I don't see what the harm is in crossing or not crossing.

When a ped breeder says they breed to preserve/improve their breed, I think thats great, but that to me is a reason to do it their way, it is not a reason not to do it another way...if ya get what I mean.
To try and clarify, I don't understand why it is bad to cross, I only understand why it is good to pure breed.