Controversial subject? We'll see.
Most vets don't recognize vaccines given by breeders or owners and most boarding facilities I know of also will only accept vet-given immunizations. This can cause some disgruntled people as they have to get vaccines done again through a vet if they want to board or groom their pet. Some vets may also not allow unvaccinated pets to stay in the hospital for simple things like spays and neuters without proper vaccinations. I've known a lot of owners and breeders who have gotten upset in circumstances like this and I've had to try and explain it to them. There really are very valid reasons, and it's not about the vets trying to squeeze more money out of people.
I will be the first to admit that giving a vaccine isn't rocket science and I can train someone to give injections just as well as I can. It's also common for most people with horses, cows, goats, and other livestock to give their own vaccinations rather than going through a vet. In most states of the US the rabies vaccine must by law be given by a vet, but other vaccines are not legally mandated. So yes, legally an owner can give their own vaccines (other than rabies) without breaking the law. You can easily purchase distemper and parvo vaccines at feed stores or online, so they are available to clients.
With this in mind, what is the problem with owners giving vaccines? Why bring it up now?
Yesterday I had an 11 month old Yorkshire terrier come in and within an hour die from parvo virus infection. A few days prior to that a littermate died at home from parvo. We managed to treat and save one of the dogs in the litter. This is a good bit older than most dogs are when they succumb to parvo. And the owner was the one giving the vaccines. In fact, the only adult dogs I've seen who have come down with parvo had their vaccines given by the owner.
If vaccines are so available and so easy to give, why are breeder- and owner-given vaccines not effective? Usually it comes down to inappropriate administration. Vaccines must be started at a certain age and boostered at proper intervals in order to stimulate long-term immunity. Vaccines must also be mixed properly and stored at the proper temperature in order to be effective. Mix them wrong, store them for too long at too high of a temperature, or otherwise mishandle them and the vaccine will not work. Also, not all vaccines are equally effective, and owners usually don't have the information available to make those decisions between manufacturers.
I routinely see breeders starting vaccines at four or five weeks old, when the minimum age should be six weeks (this is due to proper immunology). I have seen pet stores giving vaccines weekly, when a duration shorter than two weeks doesn't do anything to booster immunity. I've had clients who give one vaccine and think the pet is protected. One time I had a client bring in the bottles of the vaccine given by the breeder, where the breeder had used the diluent liquid and the dry powder from two different company's vaccines. Anyone who is in the veterinary field knows exactly what I'm talking about. For anyone who hasn't worked in veterinary medicine, please believe me that these sorts of things happen much more commonly than you realize.
When we see a vaccine record from a breeder or an owner, we honestly have little to no idea if the vaccines were administered and handled properly. Many of them might be, and I've known breeders who give the same vaccines I use and do so in a very medically appropriate way. But based on some paper or labels we have no idea whether or not that is the case. It is in the best interest of the pet and ensures the best health for a veterinarian to be the one to give the vaccines. Can vets mess things up? Sure, we're only human and as prone to failings and lies as much as the next person. But you are much less likely to have improper vaccination through a vet than through an owner. Vets simply have more knowledge and training than the huge majority of pet owners and breeders, as well as have their licenses and careers on the line when it comes to medicine and record-keeping.
I know that money is tight for people, and many give vaccines to help their budget. But you are potentially leaving your pet open to infection, as well as preventing them from getting full exams to look for other issues. It's simply in your pet's best interests to let a veterinary medical professional be the one to do vaccinations.