I am sorry people were rude to you. I don't understand why they couldn't have just put a polite "I believe yorkies should not be mixed" and left it at that
You are talking about breeding a yorkie(even if it's not to another yorkie) so it is appropriate to ask about it here.
Anyway, both yorkies and maltese are pretty expensive, whereas a morkie might be a less expensive way for a person to enjoy the breed. I think anyone can use the excuse "there are too many dogs in shelters, why breed more" That goes for purebreds too.
I am not a breeder, nor would I ever be. My husband would consider all puppies our children and we'd be forced to keep them all
I would say -
Don't breed to make money, from what I've heard there isn't any money in breeding. There are plenty of morkie breeders out there so I wouldn't breed your dogs because there isn't a shortage of morkies. Just enjoy them as pets and love them. Pregnancy and birth is hard on a dog and raising puppies and finding them perfect homes is tough too. You'd be better off buying another puppy if you want one then breeding to get one. I'd offer the same advice to any person who considers breeding. There are enough breeders out there(good and bad).
Good luck with whatever you decide.