Not the OP, but let me step in. Dog breeds are something we have created as humans, they're not wild species that need to be preserved and don't have any effect on ecosystems.
Dog breeding is largely negative at this point as most breeds have outlived their original use and are now seen as designer pets. We continue to breed them as there is continued demand, but quite often these breeds are so inbred that they have genetic health issues. We also oversupply and don't fix/neuter enough, meaning there are always unwanted dogs without homes.
I love dogs, but all of mine have been rescues and I would have no problem with the vast majority of breeds being phased out. There are still some niche cases where dogs are actually used for their breed's purpose (dog sled, search/rescue, hunting, etc) but no, I don't think a chihuahua or a pug should exist and would not be sad if breeders stopped producing more.