I’ve already been on the receiving end of sanctimony because I bought my dog at (gasp) a pet store. Fact of the matter is, we tried a shelter, but had a bad experience there dealing with surly dogs and surly workers.
"did I ask for your opinion?"
"when I want your opinion, I'll beat it out of you"
Part of the distaste comes from these pets being seen as just another commodity to be bought on a whim when wandering by some storefront.
Then, when the owner tires of them they're tossed out like garbage.
If the animal is lucky, they go to a bare bones taxpayer funded shelter where good willed people may seek to adopt them. Given what they've been through they're not always ideal pets.
But I'm certainly not vilifying responsible pet owners who do use these stores.