I know a plethora of vets that pick up these shifts for extra cash. They pay well and do provide a needed service. The exams are no different than an exam you would provide to a pet in general practice, minus if the pet is aggressive then obviously exam is limited but it would be in a GP clinic as well. Anything they find on exam that can't be addressed, the vets recommend them see a vet at a brick and mortar clinic. Heck, I know some practice owners even that do them and can then redirect some of these people back to themselves for care that can't be provided at the vaccine clinic. It can actually be a way to talk with a group of clientele that are either not knowledgeable about how veterinary clinics run or have decided they can never afford a traditional clinic without having ever been to one. You can actually advertise via these clinics, sure it might not get a lot of clients, but you will reach a few people that you likely wouldn't reach otherwise. I think a lot of people that come to these clinics are simply uneducated about traditional veterinary clinics so there is opportunity to educate more people.
A decent portion of the people coming to these clinics are your C clients or lower, more commonly among the D clients or people that would never step foot in a traditional brick/mortar clinic due to a variety of reasons. You aren't missing revenue from them going to a vaccine clinic. The vast majority of these people are your vaccine only or rabies only clients.
These clinics are vaccinating the animals that otherwise probably wouldn't get vaccinated. So I don't see the big uproar in being upset over it. Sure, you have the few well to do people that don't give a damn or want to spend a ton of money that will show up to these clinics too, but you don't want to deal with these people in your clinic either for the most part they aren't going to spend much money or drag you through the mud emotionally before spending any money.
If there is any revenue loss to a traditional GP clinic from these it is so miniscule that if your clinic is teetering on the edge and will close because of these vaccine clinics, your clinic wasn't going to survive anyway. If that is the case, it isn't these clinics tanking the business, something else is up.