But I do know why people buy bulldogs. They're easygoing. They have high medical and upkeep maintenance costs, but very low day-to-day costs. They're suitable for families with small children or other pets. They're grateful for play time when it's available, but not harmed by prolonged inattention. They're not so big that you couldn't own one in an apartment.
If there's another, healthier breed with the same characteristics and no major health problems, I'll concede that people should buy that breed and not the bulldog. But I don't think that's the case.
Stipulating that you can only get that package of attributes in a health-compromised breed, I don't think you have a very strong argument. If you need those attributes in a pet, your alternative to a compromised dog is no dog at all. While I wouldn't go so far as to claim that bringing a genetically compromised dog into the world is an ethical positive, I can't find a way to it being ethically negative. It seems pretty neutral to me.
Obviously: to responsibly acquire one of these dogs, you need to be educated about their issues and committed to ensuring their comfort as best as can be done.