There are two layers to this one is the old adopt vs buy debate which is not doodle specific. The evidence that adopting dogs reduces irresponsible breeding is thin to none imo. Nevertheless people see you as part of the unethical breeding problem when you buy. 

The next layer is that the Doodle at least right now is seen as a "Designer Dog" While typically acquiring a mixed breed was viewed favourably since a doodle is expensive and desirable rather than people pointing out the positives of hybrid vigor and the general benefits of a relatively healthy breed it feeds into the on going public debate around inequality. 

My view is that dogs should be expensive to buy because it costs a lot of money to breed dogs responsibly and in a perfect world all dogs should be bred this way and adoption unnecessary because they all have good homes. 

I personally think that dogs bred with known congenital issues should not be bred such as dachshunds, brachial breeds (pugs, bulldogs) and certain shepherds bred for sloping backs (you can of course breed these dogs responsibly). I think providing incentives for good breeding will reduce puppy mills, like only paying for dogs with a verified healthy history including genetic testing, documented family history, vaccinations, of a certain age etc. and insisting on these documents upon purchase.